I don't have much info on BTN, only 30 hands so nowhere near enough for stats to be useful.

PokerStars - $0.10 NL - Holdem - 7 players
Hand converted by PokerTracker 4

UTG+1: 106 BB (VPIP: 12.50, PFR: 4.17, 3Bet Preflop: 0.00, Hands: 49)
MP: 101.5 BB (VPIP: 13.79, PFR: 10.34, 3Bet Preflop: 11.11, Hands: 31)
CO: 38 BB (VPIP: 33.33, PFR: 0.00, 3Bet Preflop: 0.00, Hands: 3)
BTN: 255.5 BB (VPIP: 0.00, PFR: 0.00, 3Bet Preflop: 0.00, Hands: 7)
Hero (SB): 98 BB
BB: 34.8 BB (VPIP: 28.57, PFR: 0.00, 3Bet Preflop: 0.00, Hands: 7)
UTG: 109.9 BB (VPIP: 42.86, PFR: 0.00, 3Bet Preflop: 0.00, Hands: 7)

Hero posts SB 0.5 BB, BB posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has K A

fold, UTG+1 calls 1 BB, fold, fold, BTN raises to 4.5 BB, Hero raises to 12 BB, fold, UTG+1 calls 11 BB, BTN calls 7.5 BB

Flop: (37 BB, 3 players) 5 T 3
Hero checks, UTG+1 bets 7 BB, BTN raises to 44 BB

Is this a call with the flush draw? I insta-call with the A . Or do I just let it go with another villain still to act?

I would let it go pretty easy. I'm on mobile so don't have stove, but only against Asx you're favorite and other guy (fish bc of limp) is still left to act.

probably close

Bigger pre
As played c/f
With As it's probably a b/c

3way u should be snapmucking,heads up would be somewhat trickier