joxsjpxs, try posting that question to the forums -- you'll get more responses that way.

A wrist control 2-on-1 grip is much easier to escape than the pistol grip 2-on-1 version. Additionally, there is a whole series of sweeps (cross arm and belt sweep) and pass defenses that rely on having the pistol grip and cannot be reliably executed with wrist control. If you have the gi, Marcelo always teaches to focus on getting the pistol grip version.

The way Marcelo teaches this grip, you need to cross the opponent's wrist beneath yours so that they cannot reach your sleeve or collar. Once you have this they will have a very hard time passing your guard because they only have one free hand to either post on the mat (for balance) or on you (to control the distance); they can't do both at the same time.

Note that if you're both standing, the opponent won't need to post on the mat to accomplish their goals (of taking you down or not getting taken down). Therefore, their free hand will probably try to grab your collar. If you want to stay standing with them instead of pulling guard, it's important to use your elbow (the one with the pistol grip) to knock their free hand away when they try to grab your collar.