I'm using the gtech-pro/competition which currently is sold as the gtech-pro RR. It's very consistent and quit accurate compared to a dragstrip . I'd stay way from the gtech-pro SS since it doesn't have road race mode and also does not have the ability to download data to the PC for analysis . To be honest if I was looking for a datalogger now, I'd probably get the Race logic vbox mini (
http://www.racelogic.co.uk/?show=VBOX-Products-VBOX_Mini) .