Several years ago, I added a Shield RMS to a P-01.
It's the lowest optic I know of, and the bolt pattern is narrow enough to allow direct mount without a plate so the stock sights can remain and serve as lower 1/3 co-witness. However, a glass lens is optional extra making it pricey.
The new RMRcc seems much more durable than the Shield, and it's narrower hole pattern (vs. standard RMR) should also make it able to direct mount without a plate. However, the RMRcc is about .200" longer than the other optics in the micro class and won't fit the same cut, may be too long to fit between the stock rear sight and ejection port, and will probably require taller sights to co-witness over the taller optic body. Although new and not fully user tested, it's hard to deny RMR reputation for durability. It will be interesting to see if someone tries this successfully.
Another option to consider is the Holosun HS407K-x2 or HS507K-x2.
Solid aluminum housing, glass lens, slide-out side battery compartment, Motac motion activation or full-time on, and the 507K features circle-dot or dot only. Much lower $ than RMR and recent testing report by Sage Dynamics seems very favorable. I just had my SIG P365 milled for one and really like this combo.
