ive had people tell me to get the o.s. .21 rg and ive had people tell me to get the thunder tiger pro.21 that the tiger is a faster better motor....if u could find it i probly would buy it..but i cant find anyone that sells it...ive been on acehobbys web site looking for dealers..everyone ive gone to donest have it on there web page.....u guys give me your input on your trial and errors...i seee the thunder come with a roto start....o btw i have a mbx comp..and the force .26 is weak my tmaxx runs way better