I asked Rob about this today while sorting some upcoming options - certainly not standard on the fretted RAs. Rob has found that the one piece saddle can get pretty close for intonation, and in reality you can get an instrument *perfect*, and then change strings and it may be out. Or just over time it can drift.
I always thought that fretless was really what RA basses were about, and while I still think that is the signature sound, I'm finding a lot more love for frets on one as well. I think the key is the piezo - it speaks differently than a mag pickup. When I listen to my RAs in a mix, I notice that while I don't have the grind aspect of the roundwound attack, I actually have a quicker and more pronounced thump from the RA. I find that ghost notes kick more, but more from a feel than sound if that makes sense.
At any rate my new Mouse is moving along, so my current one will likely find a new home soon. Then I'm pondering a Solid 4 and maybe a fretted MB-2 5-string. Then I'd sell both my Zons and just have a quad RA attack. Good thing I sold the XITS guitar amp for a profit