I did not mind the feel of the Vita as it came, but after several folks on this forum recommended the trigger grips to me, I picked them up (this weekend). I must say I am very happy that I did. They feel nice (and natural.) They make it feel much more like holding a PS3 controller. They also provide a more "sure" grip, alleviate some of the discomfort I felt after a long gaming session, and make the R and L buttons easy to use. Some folks had posted on these forums about issues using the R and L buttons if they were not pressed squarely in the center, these grips eliminate anything like that from becoming an issue.
The last thing I will say about the grips is that they feel very high quality and fit snugly on the device.