Sweet Tart is mono. The Coconut Cream seeds I have seen germinate have been coming up poly, which is odd as its parents are both mono.
If you hsve plenty of time and space and want to pkant seeds for experiments or just for shits and giggles, then great but otherwise why are people planting seeds? With the time, effort and aforementioned space, just buy grafted trees. They are available and while they may cost more for some, it will still save monetarily in the long run.