And Fidelacchius is a Katana.  Couldn't have come up with a much better picture if I'd wanted.

Bob with Harry could quite likely result in something like...
Mab: "Knight, I command you to surrender that skull"
Bob: >dies<

IIRC, Bob did something to Really Anger the winter court a while back.  His coming back into Harry's possession could be Very Bad for him.


Bob w/Butters OTOH is pretty awesome:

I don't think so. I think Butters will keep Bob for at least several books.  I mean just look what he did with Bob's help in only a few days of consultation and cobbling together of stuff.  Before Ghost Story, Butters didn't have a lot to bring to the table in support of Dresden and the others.  He had medical training to patch up holes, and investigative knowledge regarding causes of death.   That was it really.  Well, that and a pair titanium cajones when he needed to. (SUE!!)  But really, the Hole Patching job is usually an after-the-fight kind of thing, and the medical knowledge was usually an Act 1 reveal kind of thing.  After that though, Butters would usually fade back into the background. 

With Bob though, he is participating directly.  He is taking his brain (considerable) and applying it to this new area of reality, and coming up with spectacular things in no time.  He has become the Magical Q to Harry's James Bond.   

Indeed.  I believe in the DFRPG, they also mention that its POSSIBLE for someone to learn to use magic without innate magical senses that wizards are born with, its just Very Very Hard.  Akin to a blind person learning how to paint.

EX: Anyone can empower a circle.  What else can anyone do, given the combined mental horsepower of Bob-n-Butters?  I suspect the answer will surprise Harry quite a bit.

I also expect the B&B team to develop some way of protecting technology from being accidentally wrecked by the proximity of a Wizard, the magical equivalent of a Faraday Cage.

Q: What's the first sentence of Cold Days?
A: Mab has some unusual ideas about physical therapy.  (IIRC, could be paraphrasing a bit)

The goddess of pain and murder wants to staple you back together again after you lipped off to her.  A lot.

Ow!  Ow!   Owowowowowow!!!