What is the difference between the new Mentor XTRA smooth moderate plus profile silicone implant and the MPP?

The new Mentor Xtra breast implant has a higher profile than the Moderate profile plus. This produces more forward projection of the breast. It can be helpful to provide more fullness above the nipple areola and can be helpful in patients who have early ptosis or sagging.

The Mentor Moderate Profile Plus Xtra implant is a step up between the Moderate Profile Plus and the High Profile implant. The silicone gel is the same Memory Gel used in all round Mentor implants, however the shell is slightly overfilled to limit rippling. This is a great implant for thinner patients or those looking for a bit more fullness without the round look of a high profile implant. The feel of the implant is similar to a MP+ or HP. This is in contrast to the Natrelle Inspira Cohesive which use the form-stable type gel. The Natrelle do have less rippling, but there is a stiffer feel to the implant.

You are correct. The Mentor XTRA Smooth  provides slightly more projection than a moderate plus profile and slightly less than a high profile implant. It is also slightly firmer than the other two. I use it when patients want slightly more projection than a moderate plus profile. It sounds like you are making a good choice.