I have had great luck with an older Powertrax Lock-Rite that was in the axle I bought from One Ton XJ. I have a non-disco (88 Limited) HP30 axle, AW4, and a 231 case.
In 2WD it is invisible & quiet. NO clicks, pops etc. In 4WD it spins both wheels. :dunno: what's wrong with that? My only observation (coming from 2 years with a True Trac LS, then 1 year open front) is that it 'plows' to the outside a little in turns in the mud.
Aussie Locker is a new company, and they have theirs intro-priced at $200. I have heard that Powertrax got bought by another company, and they are having QC problems with their stuff.
Ideal for a front diff IMHO is a TracTech (Detroit) Electrac. Limited slip or locked at the touch of a button, plus provision for manual override in either LS or lock. (Try that with an ARB...got bicycle pump?)
Selectable would be nice if you spend a lot of time on the road (snow) in 4WD. OTOH once you get to know how a locker works I don't see it as an issue.