I know it's a PITA to find older posts in threads, maybe the search mechanism of buzz words like Mantis or Cliffy would work, but there is a wealth of knowledge in old posts to this thread covering protectors for MM/MMR in great depth.
That said, I do not believe that Cliffy has a Merlin protector, it is made by Pinbits I think. I installed all available Pinbits, Cliffys and Mantis protectors on my MMR. Here's the list:
a. Plastic protector set
b. Merlin protector, the one that sits on top of the hole
a. Installed the full set of protectors (4)
a. Catapult (used to be hard to find)
b. Drawbridge Edge
c. (2) Rollover Switch Protectors
d. Moat Jump
e. Drain Hole
f. Shooter Lane
Personally, I installed the combo of Pinbits and Mantis to the Merlin hole. I also installed the combo of Cliffy Moat Jump and the Mantis jump protector to the castle hole. I feel like this is the way to go. The Moat Jump Cliffy has a feature that not only protects the back wall (wood) of the castle hole but the ball rolls off the ramp feature of the protector to protect the plastic moat from a falling ball. A good design approach by Cliff. All details are in older posts here probably 2.5 years ago for my install posts, that's when it was fresh for me to write about.