He has pretty good defensive numbers when you look at the advanced stats--he is an above average rebounder and his defensive +- is good. One thing to note about Mast in particular was Bradley was a really good team this year and he was their best player. I watch quite a bit of Valley hoops and there definitely was an argument to be made that Mast was more important to the regular season champs Bradley than Tucker DeVries was to Drake.
From the Athletic, who ranked Mast as the #47 transfer:
"Another first-team All-Missouri Valley player hitting the portal. Mast is a versatile Dutch big man who can operate on the block and create a shot with high-arcing hooks. That tends to be his home base, as he is ambidextrous with his finishing hand. But the more interesting skill he flashed this season was as a pick-and-pop threat. Mast hit 35 percent of his three 3-point attempts per game, with a pure looking shot that he can take quickly off the hop. He looks like a very legitimate option for a team that wants to play a floor-spacing five-man that can stretch the floor. And then weirdly he’ll be able to flash to the mid-post and drive an opposing player with an attack. The big thing that separates him from other offensive big men, though, is that he’s already been a part of pretty good defenses at Bradley. The Braves had the best defense in the Missouri Valley this year, and he was a big part of it. In total, Bradley won their minutes with Mast on the court by about 18 points per 100 possessions, and won them only by one point per 100 when he was off the court. He’s a real difference-maker that I’d buy playing at the high-major level next year."