I use a Von Ahrens one piece rest and am convinced its helped my shooting a lot. However to qualify just how much is not possible for me to do as, 1, I'm new to benchrest shooting having just started at it this season and 2, I have several Caldwell rests I've been using for years, the main one being a Caldwell Rock BR Competition purchased when I first became interested in benchrest shooting. I have no experience with top end front rests therefore, I have not had the opportunity to compare a "good" front rest/bag setup to the one piece rest I presently use.
I quickly learned that while the Caldwell Rock BR works, it is very cumbersome to use not having a true windage adjustment, and after shooting with a friend's one piece Pappas rest, I decided the one piece rest was the way to go.
Another key factor in deciding which is what type of match class you plan to shoot in, not all matches allow the use of one piece rests. I shoot primarily RBA unlimited class so the one piece is allowed however I want to start shooting vintage benchrest and will have to use the Caldwell for that as one piece rests are not allowed...
Happy Shooting,
Mitch & Shadow...