As for Carl Nagel, he’s a fantastic author. Some of his books are worth their weight in gold. Others are more basic. It depends on what you want to accomplish. Carl has a lot of books, i mean a LOT of them. Goodreads lists many of them with reviews in case you want to preview them before you buy. A good idea to figure out what you want instead of just working with the first thing you come across, which may or may not be what you want.
This is why i said years ago don’t call Andras, send him. He’s not a spirit of conjuration, he’s one of redirection. You don’t call him, you tell him to fuck shit up and point out where you want him to catch wreck. And he does.
I know demonolators want to call on the spookiest thing they can find on BALG, but Andras is not your infernal friend, his mindset is Hulk Smash. Tell him to attack a target and let him tear them to pieces and he’s happy to do it. That’s what he does best. Other than that you don’t need ANY contact with him to work with him.