So I've read a lot of comments on Reddit from both Boise and Mizzou fans in regards to him and this is what I've been able to deduce.
Boise fans absolutely do not want to lose him, and the reasoning behind it is one that would appeal to diehard internet fans. Apparently their offense looked rather dreadful for about half the season. Why that is, maybe hamstrung due to being a young OC, no idea. But he adjusted the offense to work with the talent they have and it became quite explosive. He was touted by many of them as a really good recruiter and landed the highest ranked recruiting class in MW history, being responsible for a lot of the big names himself. Recruit rankings and all that is 100% relative, but I'd imagine it's not exactly the easiest thing to convince 2 former 5 stars to play football in Idaho, and he's attributed to both of those recruitments.
He did in fact take over playcalling at the end of 2022 at Mizzou, and from what I've read, they actually wanted him back and were bummed when he left. Per them, their offense really improved with him calling shots. Again, no idea, just going off what I've read on Reddit which is a VERY large pool of people from varying fanbases.
Boise fans are pretty upset and expect their team to implode, even going so far as to say they should can their coach and start fresh. That's how much of an impact Hamdan made, apparently.
Arguing that him going to Boise 'makes no sense' is just absolutely absurd. 1.) Guaranteed OC position to call plays. He did not have that at Mizzou to my understanding. 2.) It's his alma mater. Many people on here will actively advocate for players and such to return to UK with zero reasoning beyond that's where they went to school. Sorry but UK isn't that special to where that only happens here. He played QB there and got to go back and coach there. If the cards fell in a different way, could end up being the HC at his alma mater. He had zero reason to stay at Mizzou.
I don't know if he'll be good or not, but he checks the boxes of what UK wants. Adaptability, QB coaching experience, balanced playcalling rooted in establishing the run, multi look in that capacitiy, faster tempo. There's no way of knowing who will work out and who will not, but foundationally he's there.