In reply to woolsack:
Allow me to step in, I have a Shimano 105 Stages PM.
In principal I like the idea and have no problem with the whole one leg measuring thing. DC rainmaker did some solid power testing against other power measuring units and I was convinced by the results.
Sadly it has fallen down on a couple of points.
The initial one I received drained batteries and eventually failed. No biggie as the replacement solved that however what was happening on the first one is also happening on the second one...
From some on-line poking it seems that some units have problems receiving the data and drop the signal. I have a 910xt and out of many rides I haven't had one complete ride where the signal was continuously received. This is hugely frustrating. I'm currently trying some turbo testing to see if I can do anything to get a stable signal. I really don't want to invest in getting another unit just to receive data and there seems to be a slight admission from Garmin that it's their units not Stages that are the problem. Garmin's vector system is apparently having the same issue.
So, my questions are:
Do you really need power and I mean really or are you just poking about because it's half affordable? If so then I suggest saving up double and ordering yourself a lovely UK handmade steel steed. It'll make you smile more than seeing your power numbers go flat which just makes you angry, and that's not why we ride bikes.
Are you really using heart rate and rate of exertion fully, these are pretty good and while power can add to it there are plenty of very good riders who've never touched a power meter
What's your device for gathering data? If it's a handlebar fixed job like a Garmin 500 you *might* be ok, if it's a watch type you might be out of luck - who knows! You're at the mercy of Stages and Garmin getting their act together. I can't comment on other head unit manufacturers though.
Think legacy, I've just seen the new 105 come out but I'm stuck on the old design. Not a problem just now or for the next couple of years but what do I do when I want to upgrade. At least pedals can be moved but then that's £1,200 - see lovely UK handmade steel frame again.
In conclusion
If you have money to buy, time to iron out issues, platform independent and think you really will benefit from power then do it... and please let me know how you get on