Thinking about doing a dedicated PCC for a home defense setup and was looking at an 8" CMMG Banshee 9mm upper.  I already have a registered SBR lower that I can put it on.  Just trying to decide if $720 for a complete 9mm upper is worth it and whether they are reliable.  Does anyone have any feedback or experience to share?

I've only got experience with the 45acp Banshee, but it's all been positive.
Going on 2 years and couple thousand rounds and not an issue.

Mine has been fully reliable.  No issues with using a select-fire lower.

Myself and many others have had ejector spring failures with the CMMG RDB.
I have it documented on my site here: https://c3junkie.com/?page_id=221

I resorted to a custom fixed ejector mentioned on my site here: https://c3junkie.com/?page_id=280

This is a thread discussing the custom fixed ejector here: https://uzitalk.com/forums/index.php?threads/i-did-it-fixed-ejector-rdb.97420/

I have mentioned that I finally broke my bolt with my fixed ejector after I am guessing at least 25K rounds.

Here is a recent thread discussing people still having ejector spring failures: https://www.ar15.com/forums/AR-15/Has-the-CMMG-RDB-ejector-spring-issue-been-resolved-by-the-Mk10-spring-/15-781020/

Now CMMG has released the Dissent and in 9mm they finally went to a fixed ejector but it is quite a bit more expensive.  They were able to do it with the Dissent as it uses a proprietary longer bolt and the cuts in the bolt are further away from the cam pin.  The cuts are pretty close to the cam pin on the original RDB bolt which is why they will break like what happened to me.  

The Dissent upper is great, but you have to use a proprietary endplate that precludes the use of any upper that requires a standard charging handle.  A side charger would be fine.   I think it is worth it, as it is a very soft shooter.

Be aware that even though they claim the uppers fit "any mil-spec lower" they actually don't. Definitely not the MARS-L anyway. Found this out after ordering 4 of their uppers to use on a pair of MARS SBR lowers.

Their response was pretty useless as well. First, they acted like I was mistaken, then I sent them a vid and I guess they finally got around to testing it and acknowledged it was a problem. They pretty much shrugged it off and offered nothing to make it right. I don't think they even updated the marketing pages to fix the false claim that it works with all milspecs.