2 speed for T3?

[t3 kid]

Hi,i have t3 that i use in my back yard and maybe the local track some day and ive heard that hpi makes a 2 speed for it. Does anyone else have this on there's,if so is it any good?Also, with the 2 speed on does the gear cover still fit? http://www.rccaraction.com/ubb/confused.gif

thanx,later