Improved accuracy, nothing life altering but there is definitley an improvement.
You do need to sand the power tube down.
Sand the power tube down a little bit to make sure the bolt will slide with ease. Also you do need to oil it well. Definitly worth the money, I picked mine up for 21 shipped. It did make the marker a little louder, but when I say little I do mean LITTLE. Its not going to hurt your game or anything, infact I personally feel it makes the marker sound more intimdiating but thats just my opinion. The manual states that it will improve air efficieny but I have not played enough to confirm that. I play with a 20oz tank and on my first day I only got about 400 shots through it. All in all a cheap mod that will improve the accuracy of your marker.
I am giving this bolt a 10 out of 10. Even though you need to sand down the power tube a little I believe that in the aftermarket world there is no true pefect fitting piece. Any modification you ever do to anything requires a little extra tweaking to make it perfect.
A great little mod that will help you on the field!