I have a Galco Belt-Slide for the 1911... it is very uncomfortable, and creates an un-natural draw motion. Plus, when sitting in a vehicle the muzzle gets buried in the crack where the back-rest meets the seat, not a huge problem, but I found myself cleaning excessive debris out of the end of the barrel due to this. I didn't use the holster for long.
I used my Blackhawk SERPA holster for my 5" XD-45... The muzzle protruded past the bottom of the holster, and created a similar problem as above... plus, the slide would sometimes get pushed out-of-battery. The 4" XD-357 fits much better, and is now what I primarily carry in this holster... The muzzle does not protrude.
A few other holsters which I own are also 'open-bottom', technically, but the muzzle of the gun does not protrude. I have no problems with these.
The holster which you have pictured looks like it will serve just fine, the retention strap will prevent the slide being pushed out of battery, and it is canted enough to allow a good draw from the 4 o'clock position. The only thing which you might find annoying is the 'barrel lint', if you spend much time sitting.