Saw it too, and figured it to be another snake oil. Then got curious and looked at it.
So, from the product info section at Drs Foster Smith
"Depending upon population and bio-load of the aquarium, traditional gravel vacuuming should be performed"
"One of the key components is billions of Mother Nature's own "housekeepers" - aerobic heterotrophic bacteria. These little overachievers provide all natural, stress-free removal of detrimental aquarium pollutants such as uneaten fish food and fish waste through healthy bioremediation. "
I take that to mean the stuff is likely to just, maybe, help speed up the breakdown of organic waste to nitrates. Thus PWCs still needed to romove nitrates. Despite the first quote concerning gravel vacuming, if this stuff can reduce vacuming ...... might be worth a try. But I think I will pass. LOL
Seriously, I understand what you mean about poop machines and tank "stuff" in the way. Have you tried getting a smaller end tube for the python? A couple of times someone has posted doing this. Or you can just bite the bullet and use a conventional small syphon for the hard to reach places. I use a 1/2 inch id syphon tube with a 5/8 inch id straight tube jamed on the end. Usually sucks stuff off the surface pretty good.
If you do try the Liquid Gravel Vac, let us know how it works.