Hey all, been a long time lurker but just wanted to contribute a bit as this subforum has been very helpful. I finished machining my G19's slide last night and shot 200 rounds through it today with the DPP mounted.  

Pictures

Machining:

Sorry there are no pictures of the actual machining, didn't want to get coolant on my phone.  In the picture album is a drawing of the slide cut profile using measurements from an optical comparator as well as pictures showing how well the sight mates to the slide.

Did the machining on a year old Hurco VM10i using a 1/2in AlTiN coated EM, 3.25mm TiN HSS drill, and a M4 spiral modified bottoming tap.  

NOTE: If you mount the DPP in front of the rear sight dovetail, you will cut into the safety plunger hole ( if leaving the rear sight dovetail's structural integrity intact and having a decent seating depth of the DPP).  

Milled the pocket at 420 mm/min feed, 3200 RPM, 1mm stepdowns, 10% stepover, and multiple 0.01mm finishing cuts with flood coolant for exact fit.  I spotted, then peck drilled the holes at 250 mm/min feed and 4500 RPM with cutting oil; Threads were hand-tapped using a tap guide on a Bridgeport with cutting oil; using a quality tap makes all the difference.  Tapping will leave a burr that should be stoned off or slightly chamfered with a countersink before DPP installation. There should be minimal to no burrs left by milling and drilling if proper speeds and feeds are used, as was my case, luckily.

I machined the pocket to a depth of 3.17mm which allows the aluminum body of the DPP to contact the slide a decent amount.  This is the deepest that should be cut as the safety plunger just barely kisses the 1mm thick steel plate on the underside of the DPP when the trigger is fully depressed, which acts as an over travel stop.  Any deeper and the trigger bar will catch on the safety plunger with too much friction and the slide will not return to battery.   It should be noted that I am using a PF940C frame with stock Glock parts; results may very with an OEM Glock frame.  

The 1mm steel plate on the underside of the DPP seems to be only secured to the aluminum body using a double sided adhesive similar to what is used in current smartphones.  So if you were to mill the slide just deep enough for the steel plate to fit while avoiding cutting into the safety plunger hole (with the DPP in front of the rear dovetail), there is potential for the steel plate to shear from the aluminum body over time.  

I machined the profile ~0.01mm undersize for a interference fit requiring about 15 lbs of pressing force.  Doing it this way negates the need for milling circular bosses that interlock into the steel plate.  However, having the interference fit causes the adhesive between the steel plate and the aluminum body to pull apart when removing the DPP from the slide.  Repeated disassembly could affect the waterproofing of the sight.  I didn't refinish the slide after machining as the DPP covers the whole machined portion of the slide; instead I coated the mating surfaces with green Loctite retaining compound to "bed" the optic to the slide.

One thing to note with the M4x0.7 screws provided by Leupold is that they extend only 2.2mm from the bottom of the sight, which is only about 3 threads of engagement.  This sucks from a machine design standpoint but it seems to hold up well from other RMR and DPP installs I've seen online.  I drilled the hole on the extractor side 4.2mm deep (after the 3.17mm profile depth), which protruded halfway into the extractor plunger spring hole in case I wanted to use 2mm longer screws in the future.  Using the optical comparator, the the mounting holes on the DPP for the M4 screws both measured ~4.02mm, meaning if you mess up the distance between the tapped holes, your screws will probably screw in cockeyed and reduce the pullout/mounting strength.  
Overall the whole thing took about an hour, including CAD work and CAM programming, so if you're looking to get your slide milled it might be best to make friends with a machinist.  

Initial impressions:

The sight was purchased from Optics Planet through Amazon.  I got the triangle/delta reticle version for about $350 shipped.   There were no failures at all with 200 rounds consisting of WWB, Freedom munitions, and 124gr reloads.  

The screws remind me of stuff found on airsoft guns.  2 of the 4 screws holding the steel hood on are mushroomed from overtorquing, with one of them slightly stripped.  The two M4 mounting screws had a pretty loose fit with the included Torx driver, with about 20 degrees of rotational play.  Maybe I'm just spoiled by stuff from McMaster-Carr? The finish on top of the screws has already worn from installation; hopefully they are stainless otherwise I can see them rusting if carried AIWB.

The steel hood doesnt protrude past the aluminum body in the front of the sight, meaning you'll mar the anodized finish everytime you try to rack the slide using the optic (for the safequeen types).  I don't plan on dropping my gun any time soon so I can't say anything about shock resistance or if the steel hood is "worth" the weight.  

Shooting with the  triangular reticle is great for my mild astigmatism as I can actually see a crisp triangle, whereas I always see an asterisk instead of a dot with other sights.  Ghosting is an issue when transitioning from indoors to outdoors, but it could just be my astigmatism.  The elevation and windage screws are easily adjustable; I just used my thumbnail to adjust them for zeroing.  I don't have any hard numbers regarding groupings or accuracy improvements, but I can say that it has reduced my grouping sizes to the point where I notice significant POI shifts when shooting different ammo at 15 yards.  Otherwise I don't think there;s much else that can be said that isn't already out there.  

Hope this has been helpful