I have found the Sporter version to be just as precise, though a tad more complicated to retrieve data, it can be manually transcribed, OR it can be downloaded via a pad/Iphone. If you do a lot of shooting and load development with the chrono, then I'd step up to the V3.
the v3 is worth it because the mounting choices and seeing your data also data is saved on a memory card so you just plug in to the computer to get all your data.
now that said if you just need velocity of your loads for drop and what not and you don't do a ton of load developement or keep track of all your data the sporter is fine. it can't use the rail mount feature which is a plus if you use long rails with short barrels.
btw primary arms has 10% off all magnetospeed stuff with coupon code summer