When grip shift came out it was good but Sram also need something for people out there who don't want an extra 2 inches up on there handle bars as well as the phantom shifts when your hand happened to slip. Luckily they began producing trigger shifters and they happen to do it really well. The mechanics of the shifting is great it goes as fast as you can and super crisp.
The smaller shift trigger is easy to hit accidentally, causing unwanted shifts, which can be a real pain. It can be a little awkward to swing your thumb around the big trigger, though this is a minor complaint.