I would be very happy with him, from what I've seen. Has great size for a PG and looks to have an all around skill set and knack for getting to the rim. Looks like he could legit take a SG role alongside Rondo and provide passing still from that position.
I know there's the "competition" question but I think that can be a little overrated. Especially if you see them step up in play against top competition (which Exum has done so far).
This guy is so young and he looks like he could be Penny esque. I think by the time all the pre draft business is done, he's a top 5 pick. I'm starting to become happy with this draft out to like the 7th pick, but if it was me just right now, I feel like I'd want Exum 4th if we were there. Like I said, I think he could play SG (or PG, depending on how things go with Rondo).
For me right now, these are my order and the players I'll be happy if we get:
1. Embiid 2. Wiggins 3. Parker 4. Exum 5. Randle 6. Gordon 7. Vonleh