I dont have one right now, but I plan on getting one sometime soon. I have a small tour coming up and that means being in venues that im not familiar with. I have no clue how well its wired or whats been invested into their electrical system. Because this tour is small, im not gonna be at top notch venues, so im not expecting top notch electricity.
It can quiet down your rig, specially if you know your electric outlets arent too great or consistent. But some people with a good electric system wont notice much if any difference in noise or tone.
But for the protection and consistency, I say they are worth it. Im willing to spend thousands on an amp, I dont see whyd I want to cheap out on taking care of it.