The standard Qloader socket, which is sub-par compared to the custom mounting socket.
I use a SIM-4 with sniper barrel, A2 handguard, Harris bipod, single trigger, Ariakon red-dot scope, Palmer Stabilizer, ACI remote with slide check, and an 88ci 4500psi HPA tank. I also use a SIM-5 with RIS vertical grip, deluxe tac-light, Palmer Stabilizer, ACI remote with slide check, and an 88ci 4500psi HPA tank.
You increase your mounting options greatly.
There are no weaknesses when comparing it to the standard socket.
For all of you current Qloader owners, the custom mounting socket is a must have. For those of you wanting a Qloader but didn't like the mounting capabilities with the standard socket, this will change your mind. There are three mounting brackets included with the custom mounting socket: one that you can attach to the grip frame of your marker, one right angle bracket that you can attach to a cylindrical object on the marker (barrel, foregrip, regulator, etc.), and one straight bracket that is also used for cylindrical objects. The socket itself swivels for even more flexibility when mounting. It also includes two brand new feed tubes, a new accessory kit, and a new elbow. Those are all a big help if you've already butchered the parts you already had (mainly the feed tubes). For the price of $35 I don't see how or why you would go without the custom mounting socket.
If you own a Qloader and need/want more mounting options, you cannot go without the custom mounting socket. For those of you who don't own a Qloader, you might want to check out their website. They have a very nice video of a Qloader handling 30bps.