So much of this depends upon your situation, that it almost matters not what any of us say. True, the majority of posters, most well seasoned shooters have said to get a range finder first, but consider the reality of your personal situation before buying either.
If you live out west and are shooting often at distances you cannot confirm or find that the places or matches you shoot don't give you usable distances to target, then get the range finder.
If if neither of those scenarios are true, have you had trouble at distance with your wind calls and are unsure about your ability to make a wind call that will get you on target first shot? Then get a basic Kestrel to help you learn how to make wind calls.
I live in Florida, where LR shooting is rarely at unknown range but wind is your number one enemy. If I'm shooting a match, I hardly want to throw the 1st shot (usually worth more) to find my wind call if I can put that first shot on target.
I currently have both, but use my range finder more when I run matches now and am setting up stages. If running an UKD stage, I don't allow range finders anyway. As a learning tool for a new shooter, I think that a a Kestrel has more value. This, after having purchased my first Kestrel just recently. I learned wind calls the long and hard way.
FWIW.