I just bought a Behringer HA400. According to a guy in youtube, a simple mod can make it worthwhile. I'll post results if I can measure the difference before and after the mod.
My 8-Ch. Behringer Headphone amp died after about a year and I switched to the HP4 with no complaints. It's been working flawlessly for almost 4 years, gets nice and loud, and sounds better than the Behringer too.
I use a Behringer one but was considering replacing it with something with more channels so I can give band members different mixes. That alto ones looks to be perfect, I'll probably get one in a few months once I drum up some more work that needs it.
I've noticed with the behringer that it starts to distort at higher volumes and it certainly is duller sounding than taking the headphone out directly from my Fireface. Gets the job done though and has never given me problems after a couple of years of use