For what it's worth, I questioned the placement of the rear sight, in front of the RMR.
The first place I saw red dots on slides was one where they promoted glocks and RMRs on glocks and they placed the rear sight behind the RMR (just like the BUIS on my AR15 is behind the optic.) That seemed "normal/right."
On the other website folks "made fun" of putting the rear back up sight in front of the RMR vs. behind the RMR. Various reasons were given.
I "talked" with Primary Machine by e-mail a few times before deciding to have my P09 done. Face it, the purchase of the RMR and the work totaled more than the cost of the P09. Putting the back sight closer to the ejection port was different than what I was used to seeing.
I can say now, after some dry firing and that one range trip (hope to change that to two range trips today) that the back up sight in front of the RMR is no issue for me. I was told (on the other forum) that the RMR would make it hard to see the back up iron sight. It does not. If the BUIS was behind the RMR does it make it hard to see the RMR? No. The BUIS is the same size regardless of placement, so the amount of RMR lens it obscures is the same = no issue for me.
I do believe the BUIS placed in front of the RMR adds some protection for the lens, being between the lens of the RMR and the ejection port. If I ever see a brass strike mark, or wipe powder residue off the BUIS I'll know that those would have been on the lens if not for being deflected by the BUIS.
I'm not a guy who spends money easily. Most folks would consider me pretty cheap. I never bought an Aimpoint till I found one on sale for $280 at a vendor. I haven't bought another one. I didn't buy and RMR till I found a couple on sale for $399 at a vendor. I like clearance sales. It wasn't easy for me to convince myself to spend the money to have the P09 machined and the new sights installed. Once I got it to the range and shot it, I'm sold on it. I just mailed out my P07 side to Primary Machine yesterday for the same work (different slide color).
I'm sold on it.