I don't have experience with the Maven doubler, but have a 2x booster from a different company that I am trying with my 8x42 binoculars. I have found the 2x device handy for a quick look, with my 8x42. Are there downsides? Sure. Do I want to sit and scan with it? No.Has anyone dabbled with the 2x optical doubler? Seems gimmicky but a guy can hope
However, if you find something with 8x or 10x and need a quick look then adding a 2x booster is a lot faster than getting out a spotting scope and tripod.
As I understand it, the optical quality of modern doublers/boosters is less critical than the quality of the binocular/spotter in front of it. In other words, if you put a doubler/booster behind your optic and it looks like crap... guess which device is subpar? Not the 2x. It's just magnifying problems with the device in front.