Oh and the muzzle velocity advantage they tout....ONLY comes with the longer barrel option, which extends out from the front of the slide.....and NEGATES any size advantage. The standard "snubbie" model has no such advantage.
Looking at their website, their XR9S model has an overall length of 5.1" with a standard barrel length of 3.35" For comparison, the Kahr PM9 has an overall length of 5.42" with a barrel length of 3.1".
So the XR9S, in spite of being a third of an inch shorter than the Kahr has a barrel length that's a quarter of an inch longer.
The Rorhbaugh R9 is 5.2" long and has a barrel length of 2.9"--in spite of being a tenth of an inch longer than the XR9S, the Rorhbaugh's barrel is about half an inch shorter--0.45"
The Walther PPS is 6.32" long and has a barrel length of 3.2". So the XR9S is 1.22 inches shorter than the PPS but has a barrel that's actually 0.15" longer.
I'd say that the facts seem to justify the velocity claims Boberg makes about the XR9S--even with the standard length barrel.
shorter at the muzzle, but longer at the back of the slide.....for about the same over all length
I think if you compare the numbers to other common, or even uncommon 9mm carry pistols, the overall length does appear to be quite short.