I have a 4250 that I bought last winter after my Raceair died. From what we used it this year it worked good but most of the time I just dial off of what my finger tells me after I lick it and stick it in the wind.
Probably going to get a trailer based system with a pager for next year so I would make you a good deal on this 4250 if you are interested.
We use a TAG unit. Several years ago we took a ride on the cart at the Indy Nationals and compared weather station readings with all we knew. Varied by 500ft. Pick what you like and dial off of yours.
I bought a used Performaire Eclipse from a memeber on here I have used it this year for references only,I used the components I already had instead of trying to switch in the middle of the season Next year I will use it(Peromaire) like thier designed to be used A freind of mine has the Kestrel like the one your looking at, it has been a big help to him