With the powertrax (aka lunch box locker), you'll have to change your driving habits. As stated, it'll lock up under torque. So, coasting around turns is something to get use to. I had the lock right locker (like the powertrax but less street friendly) for years with out any major complaints. The only issue I had was it couldn't handle tires bigger than 35's. You'll get an occasional "bang" in some tight parking lots and it's normal. I now have a Detroit Locker. I'm also thinking of possibly switching to a Detroit Truetrac because, of my decision to change the set-up of my rig. The only reason I did not choose a selectable locker is the added equipment and the additional cost. I did not want to have to worry about adding air lines or adding any additional mechanisms to make the locker work. Supposedly, the newer truetrac can handle up to 38" tires.
The other difference is the unit itself. Lunchbox lockers are installed into the existing carrier and replace the spider and side gears. Where as the selectable locker or a detroit (locker or truetrac) replaces the complete carrier. So, the install of a lunchbox locker is very easy and does not require any special tools. ARB or Detroit, does. Either install would be a good time to either replace carrier bearing, axle bearings, seals, o-rings, and possibly regear.
All of this boils down to your budget and what your plans are with the truck. With a lunchbox locker and no other changes and you do the install yourself, I'd say $300-$400 total. To have a shop do it, add about $200.
For the Detroit set-ups expect about $500-$600 to install yourself.
For the ARB, $900-$1000 for the locker, $200 for the air locker accessories. $200-$300 for install.
Additional items:
Gears - $200
Carrier bearings - $60
Pinion bearings - $60
Pinion seal - $10
Axle bearings - $60
Inner seals w/ o-rings - $50
Outer seals - $40
Master Install kit - $150-$200 (includes pinion/carrier bearings, pinion seal, shims and crush sleeve...)
Another option is to check out Marlincrawler.com or inchwormgear.com and purchase a complete 3rd member with the traction system you want and gear ratio already set-up. All you need to do is remove the stock member and install the new. The rest of the maintenance stuff is up to you...