I saw the magpul grip before, but I think I would prefer a vertical grip on a SBR. If I had a full length rifle, I think the magpul would be a better option. I've read on other boards that the bobro had a superior retention method and seemed to be really robust.
I was just curious about the differences between a regular and shorty. Is it the size of a person's hand that is the determining factor or is there more to it?
If you ever get a chance to go to or watch the magpul class videos there is a method to the madness of their forward grip.
The vertical grip to them is more of a reference point that something to hold onto. They believe and teach that the forward grip should be farther out on the forearm and the thumb should be high and parallel to the barrel so basically you are only using the upper 1/3 of a vertical grip.
It is all in personal preference. With my short barreled AK here I still grip the magazine and use the forearm very little. If I am shooting an M4 will move my support hand farther out onto the forearm to make transitioning side to side to another target more controlled.
In answer to your question if you are going to use it as a grip only, without built in bipod and so on, then get the shorter version. You will find that the longer ones hang up on everything and are always to long unless you have gorilla hands.
If you are getting the one with the built in bipod dont have much choice there they are long anyways.
Good luck on your search.
I have no problem with the Knights Armament issue vertical grip I kept from Iraq. Granted it doesn't have all the bells and whistles like other grips available like internal storage, spring loaded bipods, and a removable space for a pressure pad, but it is rock solid and easy to take on and off. Oh yeah did I mention I didn't pay a cent for it, because if you never signed for something you never were issued it. 8)
I've got the TangoDown shorty on my S&W MP15, and it's okay. I've never owned another vertical grip, so I have nothing to compare it to.
That said, I've got a Magpul AVG in-transit, so I'll let you know in a week or so how I feel about it.
I have a shorty Bobro vertical grip and its nice. The attachment method is different than a lot of the vertical grips out there. You simply set it on the rail, twist it into place, tighten the bottom ala Knights/GG&G and you're all set. Rock solid, yet over priced piece of gear.
For the Sig 556 SBR with OEM rail its convenient because you don't have to disassemble the rail (like you do with Tango Down) to install.