Interesting card! Definitely some bad outcomes, but also some very strong ones, and the stats of the card mean even the bad ones don't hurt. Not to mention the possibility of repeating value. I like it!
It's kind of awkward for Reno/Hand Lock decks because you are already working with large hand sizes.. a turn 6 that refreshes into a 50/50 good/bad card and potentially blocks off your lifetap. I dunno. There are some really, really bad demons. And your 6 drops are already so competitive.
If there's enough support for a more Mid-rangey Zoo/Demon Lock it's really nice.. although oddly not a demon itself.
I am really happy that they give Warlock some really strong big minions, causing Warlock to get other directions than Zoo. All that rests is 1 or 2 big Siphon Soul like spells to go with Cho'gall and we're set!
Ok, so the thing is over flooding a specific mana slot isn't bad. Flooding both 5 and 6 drops is bad. Flooding 4 and 6 mana slots works fairly well, as does running lots of 5 drops. Therefor, I don't see 6 mana slot being crowded being a problem for this card.
I'm going to say this is actually very good. A 6 mana 6/6 draw a card would be good IMO. Since Kabal Trafficker is a 6/6 mana tide totem for demons, it's goes far beyond that. The only time this is below average is when there's no demons in your deck.