if you want to get into the biasing of your own amps, first off read up on it. know what you are gettign into before you go buy all the crap to do it. not that its hard or anything, its just that if you dont know the inner workings of your amp, you could do it more harm than good, your self too (there are some serious voltages going on inside there.
if you dont posess the knowledge to swap out some stuff it may be better to leave it to a tech. in the past they might have put an adjustable trim pot in there, or they might have just swapped out whats necisarry to rebias it to the necisary voltage.
but onto the item in question, as long as that is made well, its a great idea. if you got a quartet you gotta bias that could save a ton of time.
i dont mean to make it sound like you dont know what you are doing, but i can honestly say i have sent my self to the floor a couple of times messing with tube amps. if you got the knowledge and the ability, i say go for it. doing it for free is great, plus biasing is sort of a personal prefrance, if your doing it you can set it to however you want it to sound.
good luck
