The Radeka masking kit was part of my evolution in the use of masking in my process. I purchased it some time ago and I understand that Lynn has upgraded his registration system from the very crude and virtually unworkable system he had at the time of my involvement. I can't speak to the quality of his new system since I have not used it. I do know that he had a price increase with the new system. I understand that his system is not enlarger mfg and model specific...sometimes "one size fits all" works in some things and other times it does not.
In my case, I ended up designing and having built a registration system that is a modification specifically for my Saunders 4550 XLG enlarger. My system is very precise (repeatability on the order of + - .003)
Now on to the matter of masks, yes masking is a valuable tool. However it is not used by many, expecially insofar as sharp masking, because it is more involved then simply enlarging a negative. It does possess the capability of very precise control and manipulation of the camera negative information. It will allow printing of a negative in ways that are not possible with any other means. Masking can be as simple as making an unsharp mask for increase of local contrast and reduction of overall contrast. It can be as complex as the tri tone masking which I posted some months ago.
I don't know that I have answered your question. Please feel free to ask specific questions that you may have. I will try to help if possible.