95% of the time you want a solid, low profile square vise for your mill.
There are other ways of getting angles and compound angles.
My good friend spent $28000 on his 10X50 mill, ball lead screws, power feeds, the works. His vise is a 5" tilt/swivel vise (a very expensive one), and that only gives him only a small work envelope, only several inches high. He has no room in the ceiling for a riser, so he's hooped. Wasted money in his opinion.