I've used the 8 to 10 oz double buffalo butt from Springfield leather for belts and some 4 to 5 oz (unknown origin) for a purse. The 8 to 10 oz I think is combination tanned, so not a pure veg tan and the 4 to 5 oz was probably chrome tanned.
The 8 to 10 oz is very dense per square foot and I wouldn't use it for large square footage projects because it would just be too heavy. I personally use a single layer buffalo leather belt almost every day for the last 2 or 3 years. Buffalo is strong, but tends to stretch more than cow. For belts I wouldn't use it for heavy use belts / utility belts such as full size gun belts, but it works just fine for general use and light duty (I carry a multitool every day). I notice more stretching at the belt notch than with cow, but nothing I'm concerned about. I wouldn't have it under constant tension, i.e. using it to cinch your pants super tight. Burnishes super easy and patinas well.
The 4 to 5 oz purse holds up well. The thinner leather and smaller design control the weight. Burnishes super easy, so the purse develops a patina easily. Person I made it for likes it because it looks a decade old and you can see where the side of the purse has burnished just from brushing against their side consistently. If you want a design that looks pristine for longer, I wouldn't use it.