"I personally do not do comps and as such I like the locking diffs and 2 speed. Many comp drivers like simple and do not want the extra parts or weight. For them the Sport is the hot ticket. I currently have three TRX4s operational and #4 is under construction."
"I have the TRX4 kit and one of my boys recently got the Sport. Both my boys also have SCX10’s and I have a 10 and a 10.2. Our use is about 90% crawl / 10% trail.
IMO, the Sport is Far and Away the best bang for the buck. He got the blue body and it looks much better in person than in the pics I’ve seen. The single speed in the Sport is just about right (he may have put an 11 tooth pinion gear in it, can’t remember). At any rate, the Sport is a very capable truck out of the box. If I bought a new crawler tomorrow, it’d be a Sport, hands down. ……..and I’ve thought about doing just that, but don’t really need a 4th truck."
"Yes, the 2-speed and locking diffs are worth it to me. It adds a fun and new element to scale crawling. Get the kid for general all-around trailing and fun runs. If you want to comp get the Sport."
Just a list of links about the TRX-4.