I think this video covers his strengths pretty well:
Surprisingly good technique, a willingness to drop deep and work for the team, a bunch of decent layoffs and some unethical headers. Granted, the big question mark is how well he would handle the step up from Stuttgart to a top club, but his profile looks just perfect for a squad that has a bunch of quick forwards who like to score themselves or needs the occasional not so pretty can opener against a deep defense.
I'm just curious what Bayern's strategy is, because if they want a player like that there won't be many alternatives. If they trusted Zirkzee they wouldn't need to bother with Kalajdzic's agent. There seems to be a risk that they shoot themselves in the foot by haggling over peanuts out of principle.