I use both, Draggy and Gtech Pro SS. Been using Gtech products for over a decade. The Gtech uses a 50 Hz military grade GPS sensor, Draggy uses a 10 Hz sensor. Gtech with 8-9 satellite reception knows if you move a few inches, Draggy you can fool a bit off the line as it does not have that tight of resolution. Gtech does not look for slope, you can run down hill and do a fake faster run, Draggy will label a run invalid if slope is greater then 1% I believe is the figure. I’ve compared both to track timers, Gtech is closer more often, sometimes spot on to the .001 of a second, draggy within .01. Gtech can be glitchy and have memory crashes and loose all you run data but you can back it up to a computer. Gtech has software that you can look at runs side by side 4 runs wide. I use all 3 simultaneously (Gtech, Draggy, car timer) for testing of tunes, parts, technique, as the Gtech sometimes crashes on a run, usually a good one which pisses you off big time that’s why I run both. The Draggy is the standard most street and roll race guys use for 60-130 times, I have not found many that use the Gtech. The Draggy shows my 60-130 to be a bit faster then the Gtech does, sometimes .1 to .2 seconds different but consistently different so it may be using different measurement rules. The Gtech assumes a 12” roll out so depending on stage depth at the track the track will say you ran faster then the Gtech depending on how deep you stage. Draggy you have your data on your phone forever and can share on line, Gtech you can’t. Draggy you can find (probably not now with the holidays on the horizon) repackaged as new returned items on Amazon or eBay for 20-40% off new price, like $120 verse 299 for a Gtech Pro SS as I’ve seldom seen them used, reboxed, or on sale. My suggestion if your only buying one or the other and your good with .01 second accuracy look for a deal on a Draggy.