Well, Angel did have a detective agency, with low rats. sobs.
Actually, I think all three are quite different. The FK dude was on a quest to become human again, right? For Angel, that was part of the goal, but he turned it down more than once and, really, it was more about redemption. I actually think this new thing sounds, well, new. I mean, just because it's vampires doesn't mean it's a ripoff.
Of course, my feelings to this may be related to the fact that, while I like Spike, I'm not all that crazy about him and think he was a bit overused on both BtVS and AtS.
And yes, I understand, joke, but sometimes I just can't help myself, especially when I'm so far behind on both Natter and Bitches that this is pretty much it for a while.
Edited because I screwed up on the simple html and didn't even notice. And then screwed up all later posts because I forgot to close the tag, although at least I noticed that one right away. I think I just lost all my geek cred.