What's the black templars play style?

Im currently a custodes player but looking for a second army i can slowly work towards if I find good deals such as second market and im looking for something that plays different than custodes. I was drawn to dark angels because of the aesthetic but they seem to play very similarly with tanks deathwing knights. Right now I'm looking at tyranids and sisters but the the looks of black templars but don't know how different they would play.

Tldr: how do the black templars play especially compared to custodes.