ARB is activated manually via air pressure. So you need on board air.
Good because you can turn it on and off anytime you want. And this is a great thing if you are considering
this locker for the front.
Bad because the installation is more complicated than other diffs, and there are more things
that can go bad on the trail. Also, more expensive.
Detroit locker is automatic. And will lock on the trail when needed.
Good because there isn't any buttons to push, and install is easy.
Bad because makes noises on road... tack tack tack, or click click click.
not recommended for front axle.
Detroit TrueTrac (TT) is not a locker, but a limited slip differential (LSD). So you will get some torque transfer from side to side as needed, but won't be the real locked up differential. It's better than not having anything, but still "limited." TT seems to work well in the front axle.
Powertrax LockRight works much like the detroit locker, but uses the stock differential housing, which is not nearly as strong as the ARB or detroit housings. Currently being tested, and driving impressions will be posted soon.