I’ve got one, great little device for then money and I’ve no reason to doubt the figures. DC Rainmaker likes them and the only issue he had with them (cobbles) has since been resolved in a software update.
Setting them up can be a bit fiddly but the more accurate you are in the set up the more accurate your results so worth spending the time on.
I’ll second that about the support from John Hamman, the head of velocomp, if you have any issues post it on the forum and he’ll be on it straight away.
The Isaac software is great and potentially useful if you know what you’re looking for but generally interesting anyway. You might think you’re good at hiding in the pack but the numbers might well show otherwise for example. The ability to check CDA is also potentially useful, not just for tt’ers but racers in general and even normal riders if they’re serious. Being able to swap between bikes is also handy.
The powerstroke add on looks good, never used it personally but can see how it might help pedaling smoothness and efficiency especially? if combined with the CDA function and/or a bike fit.