For starters, I'm not completely convinced that I 'need' a power meter. I'm not sure the expense is really worth it, but I am a Strava (premium) user and I do sort of enjoy the stats. I am motivated by seeing the numbers and if it would help promote my fitness goals then maybe I should be at least paying more attention to what it would take to achieve that.
If I just had one bike to setup this may be less of a problem, but I ride my 2015 Cannondale Synapse aluminum 105 for the vast majority of my miles. I also have a 2015 Cervelo R5 Dura Ace that I try to preserve for the occasional weekend ride and events like century rides, etc.
I can do some wrenching on my bikes, but digging in to this has my head swimming. I know that pedals would be the easiest solution for swapping between bikes, but I'm not sure how much swapping would be advisable. I could understand making a swap with the change of season, but swapping pedals a couple times per month seems like that might not work out in the long run.
I also run SPD pedals on my bikes. I really only go for distance and so far I've just favored the SPD. I just can't imagine going on a 100 plus mile ride and being in the middle of nowhere stranded on those road bike shoes that you can't walk in. I've got a nice pair of Sidi mountain bike shoes that seem plenty stiff. I would consider switching to road, but that's an added expense to the mix in the least to buy new shoes and switch to road shoes. I'm aware that Garmin has the Rally XC pedal option, but man those cost almost as much as my Cannondale cost me back in 2015.
I might also consider that both of these bikes are getting to be a little older now too. I could conceivably keep maintaining them for the rest of my life, but I'm sure at some point I'm going to get an itch to try something else. That just lends more to the argument for going with pedals.
Otherwise, these are the best 'solutions' that I've found so far. I actually asked the sales dept at Power Meter City and these were their recommendations based on what they sell.
For the Cannondale with the BB30 FSA Gossamer cranks:
Stages FSA SL-K BB30 Power Meter Or
power2max NGeco ROTOR ALDHU Road Power Meter Crankset
For the Cervelo:
Power2max NGeco ROTOR 3D+ Road Power Meter
Those could total between $1k and $1.3k to setup both bikes and that's not even providing a true dual sided power measurement if that is even important in the first place.
I'm a little surprised that there isn't a less expensive option for the Cannondale. I'm not entirely sure why I would spend $540 for a single sided crank arm solution when I might just upgrade my entire crankset to a 105 with whatever adapters the BB30 might require? My old FSA cranks have seen quite a few miles at this point. Something like this:
PRECISION PRO Ride Ready Power Meters
I do see that there is information that the Shimano crankset power meters just aren't very good on the drive side. They're probably just 'too stiff' for a power meter gauge to work. The 105 is probably the worst from a design standpoint as far as that goes because it is just so beefy.
I could also skip the Garmin pedals and go with these instead:
Favero Assioma DUO Power Meter Pedals
Just find some nice road shoes and only swap for the occasional event.
I apologize for the long post. I guess I probably have to decide for myself if it is worth it or not to a large degree. I am curious what others might have to say about this particular situation. Some of you guys know way more about this than I do.