I have weaned early (3 months) before. I would only do it if it is absolutely necessary...if the mare is being dragged down by the foal, for example, despite a quality feeding program. I would make sure that the breeder is feeding the foal a foal-specific feed either in a foal feeder or in a creep feeder. safeChoice is NOT an appropriate feed for a weanling foal. Basically, it just isn't very nutrient-dense, and you'd have to feed a LOT to meet a growing foals' nutritional needs, and that may be too many calories for your baby. I would suggest a ration balancer and good quality hay, if nothing else. Just MHO.
Anyway, it isn't so much the nutrition that would worry me, but rather the foals' lack of social/emotional maturity at three months of age. Social interaction is important in a young foals' development and the trauma caused by early weaning could cause ulcers, behavior issues, etc.
*I*, personally, would make sure that you have a buddy available for the foal once he gets to your farm. A quiet, older "baby safe" broodmare or gelding would be OK, but another foal would be ideal. That isn't to say you shouldn't handle the foal every day. It will be very, very important that he gets handled, even if for 3 minutes each day...halter and lead, pick up feet, lead him in from the pasture in the evening and back out again in the morning, etc.
Proud Breeder of Trakehners and Anglo-Trakehners