I have tried them exclusively in my SET amps. The main disadvantage I found with the acme and hifi tuning ones were they really didn't do anything positive in the mids. Most benefit was heard on high frequency. I thought it odd that they were marginally better than RadioShack slow blows in mids. Also the biggest beef I have with the Acme fuses is that they actually blew for no reason sometimes when I'd turn on my amps. I can understand if I had te wrong value or if it blew for legitimate reasons, but these suckers blew for no apparent reason. YMMV.
The Furutech fuses are the best of the bunch if you don't use te AMRs. The only flaw I found with the furutechs was that highs were a touch 'supernatural' sounding. Sort of artificially detailed. The AMRs are detailed, but they don't try to draw attention to themselves of that makes sense.
As far as where to buy I wish I could help you. I bought mine directly from the AMR reps at RMAF in October. I figured they were readily available.