If you want to shoot a string loop, I would just get the standard scott caliper. I went a little overboard, and over the years have acquired a Scott Caliper, then a Little Goose, then when the loop became a factor, I bought their loop specific release, which has a slot with a little curved piece that fits over the end.

All these releases are great, but you have to look at them in three ways:

How do they set up to your hand and what features do they have. The caliper is nice, but will give you a slightly longer reach to the string which might be a factor if you felt your draw was short already, we are just talking a 1/4" I would guess. the little Goose (LG) is the opposite, it almost lengthens your draw, but be careful, it might feel awkward if you want a lot of finger extention. Both of these have a barrel swivel that means the head can be rotated to any position you want. This is my main gripe with the loop release, in that since the loop is flexible, the barrel is fixed on this model. Just because the loop will twist a bit on its own doesn't mean that is the best place for rotation to occur, so that alone is a bad feature in my mind.

Finaly, how does the release set up to the string:

The caliper was designed before loops were a factor, so it can be shot off the string, but it is my favorite for a loop also. It releases the string down the middle, and has the widest opening jaws which is great for aquiring the loop during hunting situations. Flipping the trigger back and forth opens and closes the jaws. The LG works the same, but was specificaly designed to flip the string a little on the release, the way a finger shooter does. The idea was that a caliper might release the string a little differently every time, but that the LG, with only one jaw (same deal on the mongoose) would always push the string out to one side, and be more consistent. Currently this is my favorite release for shooting off the string, and it is so accurate I don't see any advantage to a loop. I wouldn't use it with a loop, since the loop is supposed to increase accuracy in the same way, though a person might want to if they needed more length, or had small hands. The loop release was designed for loops, but is awkward to use, has a nasty feeling trigger etc... no improvement in my view. It also won't open and close with the trigger, and loading is a two stage affair.

Overall I would recomend the mongoose or little goose off the string, or if you want the loop, use the standard caliper. Better still though twice the price would be the TRU Accutouch jaws with a loop, or the single ball version, without a loops using the proprietary single ball.