I had one in my old Bluesbreaker Combo in place of the GZ34 rectifier. Noticeably tighter and faster bass response. Didn't really notice a difference in output or headroom. Also tried the Copper Cap. Much preferred the tube rectifier. The Copper Cap sag felt exaggerated. Didn't feel as natural as the tube rectifier.
I've used them a few times and generally liked them when I was into faster attack. Just be sure it doesn't throw your B+ up high enough to melt you power tubes and have your amp rebiased when you install it.