I have not been using "mast protectors" for many years as the newer boom clamp designs do a much better job of "spreading out" the concentrated load over a larger surface of the mast.
I think the boom you may be getting has the plastic flap on the back of the boom clamp (similar to a Fiberspar) so that will spread out the clamping force adequately.
Do check to see if NP recommends the use of a mast protector though.
You won't have a warranty as the scond owner of these newer items, but if it recommended by NP it's probably a good idea.
I do use the RDM adapters and I was using one today and had a lot of trouble getting the boom on and off as this was a newer HPL with a similar "plastic flap". I'll use a different boom with the RDM's in the future.
Hope this helps!