I tried a couple of those stays a year or so ago in an attempt to do away with the bent wire thing across the boot. I didn't like the idea of bolting it to the rear deck channel so made two plates which bolted to the engine/wheel arch bodywork inside the engine bay. I also found a lot of experimentation was required to hit the sweet spot for opening/closing and must have spent two or three days messing with them.
When I got them something like working I found they would rattle when closed, which really pleased me.
And so in the end I gave up and went back to simple 1/4" rod supports, but this time mounted across the luggage tray on the engine side so they aren't so much on show.
If you want that sort of mod, then I think a pair of low load modern hatchback struts on a framework under the lid would be better. You still have the problem of siting them of course, but it's a more elegant approach.
Brian