The HTT amps & voice modifiers have always been junk and that's mainly where they fail.
My Hovi setup volume output is pretty decent (given its size). When used with my amp or something like the ROM/FX it works quite well, though as Ollie has stated it's not as loud as most chest mounted systems.
For the record I've never stated my system is as loud as or better than a chest mounted system. Comparing my system to a chest mount is like comparing apples to oranges. My speakers are 1/2" in diameter with a maximum output of 1w @ 90db, a standard chest mount system speaker is 1-1/2", 4-6w @ 140db output however, if you want a audio system that is completely contained in the bucket my system is still a viable option, yes there is a small sacrifice in sound level but some troopers like my self think it's worth it.
Bottom line, you want it loud enough to be heard over everything else around you, don't mind a system being mounted in your chest and a wire running down your neck then a chest mount system is for you. if want a system contained in your helmet, with your voice that originates from your helmet and no wires running down your neck than my Hovi system is a great alternative.