I currently have a wireless Atech computer fitted to my Brompton which can be calibrated for 16" wheels if I input the 16" wheel setting of 1276. The only problem is that the magnet on the wheel keeps getting shifted slightly when the wheel folds and also it lacks a backlight. Some of the other options like the Cateye Velo 5 offer backlight but can I avoid any shift on the magnet when fitted to the spokes and also can it be calibrated for 16" wheels. Most only list 2 wheel settings on the packaging.
I think most computers now will allow you to set any custom setting as well as the presets which are likely just 700c and 26". It's good to use the custom setting anyway as the presets even for 16" don't really take into account the exact circumference based on your specific tyre-choice. You probably already know how to do it but all you need to do is mark a chalk-mark on the ground with the valve of your innertube at the bottom of the wheel then roll the bike (like a surveyer's trundle-wheel) forward until one whole revolution of the wheel has occured. Chalk the spot where the valve was and measure this - it's the figure you need to put into your 'puter and you'll get really accurate mileage/speedometer readings (as long as you keep your tyres inflated properly!)
As for the magnet; they do move a bit - maybe apply a blob of Araldite or similar epoxy glue to it once in place to stop it moving about?
And the vacuum tubes will keep your hands warm in winter. Only three functions though, 'on' 'off' and 'broken'.
I have a Cat Eye Velo 8. I don't like it much. No backlight, and guess what - the magnet keeps shifting. I quite like the el cheepo Halfrauds one on my other bike, but no backlight. Whereas with vacuum tubes......