I’ve been running them vector 3s (pair though, not single side) for almost 2 years now, maybe 3,000 miles on this bike. The initial battery caps did indeed have issues, but the second design they replaced them with has been great for me. I’ve not had any issues, even following a crash with a fairly hard pedal strike that actually caused the battery cap to spin out and get lost, as well as physical damage to some of the plastic on the pedal around the cap. Did a little cleanup, Garmin sent new battery caps free of charge, and I’ve been using them without issue in the year since.
I got them essentially new from a friend who ended up going a different direction, and got a deal as a result. I’m not sure I would buy them at typical retail prices over the assiomas or something else, unless I was really tied into the garmin ecosystem (I’m not - the pedals and Varia are the only Garmin product I currently own). But if you’re using points, credits or something like that, I think they’re a great product – just not the best value.
Maintenance has been essentially 0 beyond battery changes and periodic clean/lube as you would with any pedal.
I would note: make sure you set the crank length correctly. Initially mine was set too high and it gave me inflated power numbers the first few rides before I started thinking something was off (was my first time using power outdoors, mistakenly chocked the difference up to indoor/outdoor).