Davis has the talent and enough past history to suggest he can be Terrele Pryor, loading up yards on a hopelessly losing team. The Browns are thirsty for any sort of reliable way to get yards, so opportunity is there. Downside is that Deshone Kizer vs. Kevin Hogan is a thing. It's possible there's nothing there, or there is something, but you have to wait 4 more weeks for it. I'd feel better taking another receiver with a more immediate future because at least you can roll the dice once or twice first.
Dion has upside recently but the risk you're taking is that the Pats will continue with their current gameplan. Their coach is notorious for changing schemes when he thinks they're too predictable, which usually only leaves their goal line option (Gillislee), their 1 yard to go (Brady) and their Hulk (Gronkowski). If Gillislee is too far in the doghouse Dion will get carries, but the only way he gets the relevance he had two years ago is if he becomes their defacto slot receiver, and we haven't seen that happen yet. So I think he's a fair bench stash but then so is Burkhead. At least with other lottery tickets you can paint an opportunity plan that is not "Coach changes offense."