Huh, I didn't notice the weight, in-hand, but I was def looking for something sturdy when I bought it, anyway, for my light/camera - my Cervelo stem has the mount slot on the faceplate, but the compatible mounts weren't rated to hold more than a head unit. How much are the K-Edge, and the like, weighing in at?

Yeah, the K-Edge also weighs 50 g. I guess it's the nature of the beast. I guess I wouldn't mind so much for something that attaches to the bars and is easily removed, but I'm not going to unscrew the stem each time I need to mount the light.

Do the Wahoo plates also work with Garmin computers or do I need to replace the plate with a Garmin specific one?

Both versions are available from that manufacturer, that said...

The plates are the same, but turned 90⁰ from one another, so either would mount sideways on the opposite mount. I moved from Wahoo over to Garmin since buying the pictured mount, and was able to unscrew, turn and remount the adapter plate to accommodate my 530 - the mount had appropriate threadings and the screws were just long enough (and I used thread locker for extra peace of mind).