I tried both today and bought the CL-5 as I was looking for a broader tone with more volume than my Selmer C*; the CL-4 didn't impress me at all as being different than my Selmer or LeBlanc mouthpieces. Intonation was really good on my Selmer 9* - I think the CL-5 will make doubling easier now.
The mpc came together with a single screw ligature that is supposed to be working on these Master pieces only (or, rather, vice versa); it looks nice and works allright but doesn't have the advantages of a double screw lig.
- to be honest, I think all of today's companies really excel in marketing rather than in the quality of their products; as I am more of an amateur when it comes to clarinet playing, I might as well use one of these modern products, but I doubt if a real pro would ever go with anything that is on today's market.