momus, I think they do a fine job and I've used them on nicer cameras with nicer lenses and you couldn't tell it was a cheap plastic CUL.
The put that attaches to the Holga's lens w the notches is plastic (it's all plastic) so it's very easy to file/cut notches and flip them to rubber band them to the TLR body as I said above.
I also took it a step further and wrote the focus distance in inches on each one of mine for easy reference. I also have a piece of string w knots tied on it that I can use to get my focus distance right that i keep with the holga when I use them w it.
For $20 USD for the 2 sets, you can't go wrong IMHO.
Look forward to seeing what you do with them! (Assuming you post results)