Just thought I'd mention that I also have Lynn's masking kit - the complete system.
Regarding quality, the construction of the carrier, and carrier holder is very nice. Black anodized aluminum is the name of the game. Looks very professional.
The holder is positioned in the enlarger through a 'friction-fit' type system. On my Saunders 4500-II, I had to remove the lower portion of the negative stage (it just lifts out). Insert the holder, lock it in place, and it stays put. It's square, so you can rotate it 90 deg. for different orientations.
I've done some masking with it, and it does work well. Now that I have a new darkroom with more room, I expect that I'll spend more time working with the masking process.
While expensive, it is recommended.