Ground beef may get decent flavor but it will be short on the collagen/gelatin you'd get from bones/connective tissue.
Making stock in a pressure cooker makes it go much faster but doesn't really help with the time to brown which is important for a good beef stock.
I've used the BTB beef stock and it's pretty good. If you don't use much, I think it's a good alternative to making your own unless you have tons of time.