Since it's a plaything and you want to do it on a budget, I'd go with Detroit EZ-Lockers or Powertrax Lock-Rite's...whichever you can get the better deal on. As long as you aren't running a monster V8 and monster tires, these should work well for you...they're 'drop-in' lockers that go ino your existing carriers (BTW: Lock-rite is supposed to be releasing one that fits into Trac-Loc carriers next month). The Gearless is a compromise unit that's sort of a locker meets limited slip for those who daily drive their trail rigs. I peronally know 3 people who've blown them and there has been a recall of stock from dealers for faulty parts. None of the vehicles were being abused and they all blew on the street (one guy flat-towed from Chicago to Tellico, unhooked, and it blew as he was pulling into a Taco Bell parking lot to get something to eat).