Archer
··Omega Qualified WatchmakerThere are no disadvantages at all with the stereo loupes while the advantages are obvious. The key is quality. The PeakOptics brand I link above are of good quality and not the cheap types at all.
Quality is not the key, at least for me. These things look bulky and uncomfortable to wear for an entire day at the bench - remember even something that feels lightweight to you, gets pretty heavy after being strapped to your head for 10 hours. Even if they are not as bad as they look, they do put me personally at a big disadvantage. And given the age of the average watchmaker, I'm sure I'm not alone.
Here is what I use for general assembly work - a 4X Behr loupe attached to a pair of reading glasses:

This is what I use for probably 95% of the work I do on a watch, and I have zero problems with depth perception when working with it. I need the reading glasses to see things on the bench, to enable me to look at the timing machine while I am assembling a movement (often assembling one movement while timing another), to enable me to see parts I'm picking up with my tweezers to assemble the movement I'm working on, etc., etc., etc...
If I used one of these large head mounted things like you are suggesting, then wearing the glasses at the same time is not possible, so I would be constantly (and I mean constantly) removing the Optivisor and putting my glasses on, then switching back to the Optivisor. With my current set-up I either flip the loupe up out of the way, which takes a fraction of a second, or I just look using my left eye to do what I need to do. This might not seem like a big deal, but using one of these would make a significant negative impact on my productivity and therefore my livelihood (not to mention my waiting list!).
Again, unless you understand what it's like to do this day in and day out to make your living, I'm not sure you can claim that there is no disadvantage with using something like this. Something that impedes my productivity, feels heavy and uncomfortable to wear (when compared with a pair of reading glasses) and offers no advantage to me doing my job is certainly not an improvement.
Cheers, Al