I purchased my first power meter in August of 2010. It was a PowerTap power meter that is housed in the rear wheel/hub of your bicycle. I sold it after just two weeks of owning it. The reason for me was that I could not race with it. The wheels were heavy and it was a not a aerodynamic as other race wheels that I had. You are able to purchase these hubs in any wheel that you want, but I already had multiple sets of wheels and didn't want to buy all new wheels with these new hubs for all the different applications I use the wheels on. So I had to look elsewhere for my power measuring needs. The best out there at the time was the SRM power meter. I believe the owner of this company was the one who created the first power meter for LeMond back in the day. So these guys were used to test all other power meters to. That also means they were expensive, and just too much for my budget. There had been talk of a new power meter that was going to come out that would be housed in pedals, but that technology didn't come out to this year so I would have been waiting for a long time, and I don't know it would have been worth it. So I landed on the Quarq Cinqo power meter, a late comer to the game but they had the most strain gauges, you could change it's batteries on your own, and you could recalibrate it on your own, after buying a 50lb scientific weight and program.
The use of a power meter in my opinion is like doping when compared to those who do not use it. I'm not saying that you have to use it to be good because plenty of people do. But with the help of one of these meters you know exactly what you are doing at all times and are able to tailor workouts to see results faster. Over the span of last season I saw an increase in my power of 20% in one year. This year I am already 20% farther along than the same time last year. All of this just from knowing that every workout I do was done to it's maximum. No wasted time.
I have many friends that ride that can't ride like this. Many people see riding as a release and don't want to think about anything when out on the open road. For me it is the opposite, I go crazy not knowing everything that I can. I actually find that I enjoy riding more when I have a schedule to follow, unless I am on a group ride. I just get too bored if I am not focusing on some interval. The other problem with power is that it is not a common sense type of thing. You have to study how to read your power files, and even after reading a whole book like Training and Racing with Power there is still a lot of deciphering. If you really want it though and you know what to really look at, power meters are a great tool though.
Quarq was recently purchased by Sram, which I was happy to hear about as I am also a big fan of Sram components. This purchase has lead to Sram releasing their own branded power meter this year with a newly designed Sram Red crank specifically made for the Quarq spider. It has dropped a considerable amount of weight and added stiffness with the addition of a 5th arm on the spider. This is all from what I have read though, as I do not have the funds at this time to purchase one. I hope to maybe buy one next season though.
That brings me to my last point about the Quarq. Many people look at this crank based power meter and think it is not a good option because it is too hard to move from bike to bike. But this is untrue, and I would argue that the new crank based power meters take as long if not longer to swap from bike to bike. This is a video that I found right before I purchased my Quarq that really sealed the deal for me with how easy it is to switch between bikes. My two bike even have different bottom brackets, one is a GXB style while the other is a BB30 with adapter cups. Still only takes me a little over a min to go from my road bike to TT bike. The only reason I would like to get the new one is I would like to have a 54 or 55 tooth chain ring on my TT bike. Not really a necessity, more a desire, but I digress.
The negatives that I have found with my Quarq are that I have needed to send it in two times to have repairs done. Both times the unit was shipped to and back from their headquarters for free and was back in just a couple days. Both times they completely replaced the spider which was a nice plus as both times it was an updated model.
So if you are in the market, look long and hard at the Quarq. I think you wont be disappointed.