There are a couple of ways to play an early 43.
S (split with 24/20 13/10)
Z (reverse split 24/21 13/9)
D (bring two down 13/9 13/10) and
U (move the back checkers up with 24/20 24/21)
S is weak as an opener for two reasons - 1) by slotting the 10, you have checkers on the 6 8 and 10, all 2 points apart which gives you fewer combos to make new points than slotting the 9 2) by splitting to the 20 you invite an attack - your opponent will be less likely to hit loose on the 21 than the 20. Here, S is extra weak because of the made 4 point - we'd be slotting a fourth point in the 4 6 8 10 chain which is inflexible. So, Ill dismiss S.
D derives most of its appeal due to the extra gammons it brings. Here, we don't need gammons so I don't think D is on the right track.
U might well be best - with the bar point made we need to concentrate on escaping the runners. But I'll opt for Z. It's more balanced.