the gtp d/o roller came about because some of the guys using ofna cars found out they discontinued one of the kits that guys were using to convert. there were no prebuilt chassis at that point. some people emailed them and asked if they would toss certain items together as a package and voila. they happened to listen and its worked out good so far. the d/o package is offset slightly, along with the single speed - d/o's require it. just like 8th scale off-road's boom its trickled over to the d/os and now this is the hot class currently with average joe.
2 of my friends bought one each within the last 2 weeks and had them out on the track last night tuning for this weekend. toss in the OS 21 and they're fast enough.