Old stencil blades do work fairly well, however you can hear them scraping across then stencil as the edge finish is not as good as a proper blade. I wouldn't want to use them on a stencil I was planning to use a lot. The Aliexpress holders look pretty convincing (the same as some of mine), I'm sure the blades are alright too, I'm equally sure mine are better at 10x the price;).
The Genesis frame is a mechanical system the foil is loosely held into place with retaining bars on top of semi circular rods, on all four sides, then you flip 2 levers in the frame which rotates the rods 90degrees pushing the stencil outwards and pulling it tight. All around the edge of the stencil are lots of holes or slits. The frame is not cheap (£1k+), it is very much a system for when you have a lot of stencils all of which you want to use quite heavily. There are several rival system, some open, some closed but if you are a mechanically minded person with a CNC/box of bits it wouldn't be hard to replicate their basic function. Some systems use air which introduces all sorts of failure types from leaking valves to blown bladders. Alpha have a system where the foil comes in a very light frame which you then clip into a bigger frame, I bet you can't get them from anyone else once you buy into that system.