No, sorry haven't tried them. I am so used to wearing the velcro under belt as my stand alone daily use belt, that my pouches etc stay mounted on the outer belt seen above. So when I shoot I just strap on the outer belt. I will say that the taco pouch above with the flashlight in it is a single taco on a single modular and I might often slip it off to carry one spare mag if I am concealed. The modular rig is nice in that it makes it easy to change out the taco's for various set ups.
IMO, the Safariland holsters are much higher quality materials and mechanisms. I tend to run the ALS set ups but the ALS / SLS set ups are great also. The Safariland holsters also have a nice lining. Not saying that the G-Code holsters are bad, because I don't think they are, but I am a bit skeptical of the spring loaded set up in their XST, plus it is bulky. I think the casual user would be OK, but I would have to run the set up under hard use for a long period of time to determine the durability of the hood system.
I will note that I do have kydex mag pouches for both pistol and rifle mags. The downside which can be seen, is that the rifle mags especially take up A LOT of space on the belt. Not my thing. I don't like having the hard mags or load systems in the small of my back.
My problem with the XST is that I have to use this strange ass thumb in a different direction grip approach on it. It's like their release button is kicked back an inch or so in the wrong direction. I do not like those holsters. That said, on their non-retention holsters I have found them to be pretty nice.
I can't say that I am a fan of how the cowl is setup for the G-Code pistol w/ light holsters. The Incog holster feels really nice as well for IWB carry. As for the G-Code RTI wheel, man that thing has got to be one of gods greatest gifts to gun owners imo -- they are just utterly fantastic. For a trainer, being able to swap out holsters / guns for people was so nice!
As a side note, and I have said it multiple times - HSGI taco pouches are, in my opinion, the probably the best magazines pouches on the market. Love those things! In fact, I just bought my dad some of those as his christmas present (he's a mechanic) to hold his gerber / flashlight in.
To answer the question on the G-Code holsters, I have run through a few classes Carbine / Handgun courses and never had a problem with retention. Grant it, also, that this is a static range so we are not climbing or throwing our legs in the air to get over an object (wall etc.). My gun has never slipped out. I do have some concerns that after I added some deck taping to the top of my slide to aid my ability in clearing one handed malfunctions that I may have worn away some of the holster in top slide area of the interior, however, still no problems.