I don't usually chase speed records, but it's nice to know if I'm getting near speed limits, how far the trip was and how long did it take. I also like to track component durability. This page briefly reviews several speedos I have tested (in chronological order). All of them use the same principle of a magnet on a spoke triggering a switch on the fork, transmitting the signal by a cable. I use these abbreviations for function lists:
Functions: T, S, M, D, C
My longest-used speedo, rest in pieces. It had survived about twenty years of rough handling, then it suddenly began to reset randomly, as if power supply was failing (reason unknown, everything OK inside). Red button switches modes, yellow one resets T, S and M after a long press. There's a third button hidden on the back side which lets you set the clock or wheel size. D can be set after battery removal. S is limited to 10 hours, then it starts counting from zero again.
Conclusion: no longer in production, but if you manage to find one, it's not a bad choice.
P.S.: complete and functional socket with cable, sensor and magnet available for the first one who asks for it.
Functions: T, S, D, C
Even older computer with the same controls, socket and battery (LR44 thick small button cell) as the BC-600 (the same manufacturer), it just lacks top speed memory. It has worked on at least three bikes. Reliability is not very good, after several years and many rains the gray switching button became a random number generator, and the power supply sometimes fails on bumpy roads, resetting the memory.
Conclusion: not reliable enough for my taste.
Cheaper variant of the KCC-13 below, can be identified by silver buttons and more burr on the plastic parts. Functions are almost the same, just D can't be set after a battery replacement - a fatal flaw for me, so I exchanged it for another one just after reading the manual.
Conclusion: unusable for me, but may work just fine for someone less demanding
Functions: T, S, M, A, D, C, Scan and some other bells and whistles
Not very old (2012) computer of medium price class. I like its screw-on magnet which is easier to work with than the Sigma-like snap-on ones and works for flat spokes too. There is no hidden button at the back, settings open by left button long press (good idea). Hard reset occurs after battery replacement or after long press of both buttons (bad idea - it happened once in my pocket). D is limited to 9999.9 km which is not very much. Trip time is limited to 10 hours or so. After first real rain, the select button became a bit erratic - sometimes it clicks without doing anything, sometimes it jumps more than once. Besides that, the instrument works reliably. AG-12 battery (medium height small button cell) is rather hard to obtain around here.
Conclusion: usable, but I wouldn't buy it again
Functionally identical with the KCC-13 and with the same socket. Seems to be better weather-protected: I found the photographed specimen stomped in mud on a country path (and will gladly return it to its rightful owner) and it seems to work normally after a wash and battery replacement, although the buttons misclick sometimes.
Conclusion: see above
The cheapest speedometer available in our shops in 2014. Wheel circumference is input in centimetres and D can't be set after battery replacement. I exchanged it for another one right after learning this.
Conclusion: only for the least demanding
Functions: T, S, D, C, Scan
Speedo from the cheapest end of the range, produced by Sigma, bought in 2015. Unlike all the computers above, it connects with its socket by turning instead of sliding - it's easier and needs less space around, but can be knocked away by an unfortunate touch (happened to me once). The socket can be disassembled and put together in an alternate position, so it fits both handlebars and stems. A good idea is reducing front control buttons to one - short press selects, long press resets. Settings are accessed by a tiny button at the back. I don't like automatic switching to T after waking up from "power saving" clock mode - when riding to work in the morning, I need to know what time it is, not how far it has been. Power supply is an easy to obtain big flat CR2032 button cell. Reliability is good so far, four years of everyday commuting haven't leave any traces.
Conclusion: I'd welcome some little changes in software, but hardware is very good. I'd recommend this one.
Functions: T, S, M, A, D, C, total riding time, thermometer
Computer from the top of the medium price range, bought in 2016. Socket and battery are the same as of the Speedmaster above, probably Sigma's standard today. There are three control buttons again - select, reset, and a small set button at the back. I don't really need all of those functions, but I wanted the top speed memory which is not supported by any of the lower models of this line. There are lots of configurable parameters including language and screen contrast, settings are done in a menu. After a while of standstill, the speedo switches to power saving clock mode and wakes up in T when the bike sets off again. Resettable values can be reset either separately or all at once. During first months of use, I had to wiggle the speedo in its socket twice because it lost contact with the magnet, but this glitch hasn't repeat since then. Waterproofness confirmed. Beware of a trap: due to the variable contrast, the screen is powered by a voltage regulator, so it shows the same perfect black regardless of battery state. Then you take the bike out in cold weather and the speedo suddenly stops working and forgets all data. The only symptom of dying battery is thermometer stuck on last measured temperature; then you have about a year to empty. But I don't know if this works every time.
Conclusion: versatile, fairly reliable and recommendable. But if you don't need this many functions, the following Kellys might suit you better:
Functions: T, S, M, A, D, C, Scan
Lower medium price range, produced by Kellys, bought in 2020. Socket which fits both handlebars and stems can be fastened by rubber band or zip ties, speedo inserts by turning, upside down insertion possible. The threaded magnet fits round and flat spokes alike. There is one button at the front side of the instrument for selection and resetting and two small buttons at the rear: one enters the settings (can be pushed by fingernail), the other performs total reset equivalent to battery removal (only pushable by a pointy tool). Battery: CR2032. Current speed is displayed either in the top row as usual, or in huge digits across the whole screen (selectable). Automatic mode switching (Scan) can be turned off. T, S, M and A are reset all together. D can be set even without a total reset. No automatic mode switching after long time without inputs.
Conclusion: I'm happy with the functions and controls, time will tell about reliability.