I would just get a single-sided meter on your Cannondale, for example a Stages or a 4iii. You are right that the dual-sided crank meters on Shimano have problems.
Any extra step you need to do before a ride just adds resistance to riding, its better to have as few steps as possible. So I would skip the pedal swap. I also am with you on SPD, hate those road shoes.
You don't really need power data all the time, so starting with just one bike will be fine in my opinion. You want it on the one you are using the most often so you can start to get an idea of what various power values feel like. If you end up being super-stoked about it you can always outfit the second bike later.
If you by chance have 175mm cranks I have a used Stages Ultegra crankset sitting in my garage I would sell for cheap. My bike fitter talked me into 170mm cranks.