I'm no expert on whether it's codified as a work safe practice, nor am I out to convince anybody to get on such a rig. For what it's worth, I'm just sharing what I've learned as a sailor, and what I see here is a lot of folks certain that this is crazy because of their intuition that it'll tip over easily. With that it of the way...

Based on my intuition, there was simply no way a 747 could even toodle around the tarmac, much less fly, just by blowing some air out the back. Big ones weigh 500 tons! Then, I learned the power of air and lift intimately by putting a specially-shaped piece of Dacron up a metal pole on top of a boat. Experience updated my intuition, and I'm not even slightly nervous about flying anymore.

Similarly, from the other direction, my intuition said that there's no way a boat could stay upright with parts (mast, cabin, tuna tower, stacks of containers, water park and shopping mall deck, etc.) so high above the waterline, and so little hull beneath it. But I've learned intimately the effects of primary stability, and ballast. With my intuition changed, this setup looks fine.

I've had the experience, too, of working in a boat yard. At the end of the season, the owner drove the crawler crane onto a barge not much bigger than the one in the image, and we used it to yank boat mooring anchors out of the lake bed. Even a heavy weight on the end of the crane boom barely affected the trim of the barge. I've walked on many an EZ Dock section, and experienced that sections like this have immense primary stability, too.

Indeed, by my back of the envelope calculations, that 20' by 20' EZ Dock barge would take in the rough range of 75 tons of force to capsize. (Easier to submerge it!) Even with the 32' lever arm of the scissor lift, that's still more than 7 tons of lateral force needed to capsize it. I don't know the numbers on what it takes to capsize the scissor lift itself, but given that I know that the barge is going to stay quite level, and that there's no lateral force on the scissor lift platform in this scenario, it seems that they'd be fine even without the straps lashing the lift to the barge.

Anyway, I did a reverse image search, and did not find an original source. I have no idea how common this is, but I did find a comment thread from 4 years ago on the red site with comments from a user who said he called a local company that rents out Rotodocks (a very similar product) which claimed that they do it all the time.

Hope that is interesting, and yeah, absolutely, get the numbers from a real engineer before putting yourself in situations like this.