I have all of the backspin barrels, they all work great if you use them right (most people run their flatline with too fast of an fps, you want it to be 270fps max on the flatlines, and buy gloss shelled paint)
The flatline with an apex on it is rather fun!... I have video on my channel doing that, crazy dive bombs at 60 feet!
Here is a video I just put on my channels, with a j&j barrel and I tape modded an Apex 2 to the end... (set the apex 2 at 4 clicks) and run 280fps.
The most fun barrel is the Monsterspin, which is a flatline with a Apex 2 tape modded on the end... You can dive bomb and shoot around bunkers at 60 feet. It is insane! Here is some video of it in action.