I feel like the initial response from players on this card was way too negative in relation to this card's strength.
I think this card is gonna be quite useful in a number of dragon decks. If you think about it, control decks running this card are concerned about 2 things. Card advantage and board control. Tempo matters, especially in some match ups, but definitely a deck aiming to beat other control decks care far more about card advantage and board control and this card does both of them.
There won't be a lack of targets for sure seeing as most control decks run at least 3-4 legendary cards (sylvannas not being a good target, but hey you can target your own sylvanas). And likely we'll see ysera make its way back into the meta, perhaps even *malygos*. We already have jaraxxus, malganis, alexstraza, black knight, sneed's, kelthuzad, ragnaros, dr. boom, cenarius, tirion, antonidas, van cleef, alakir, neptulon, alakir, baron geddon, grommash, harrison jones, king krush off webspinner, malorne off webspinner, loatheb, toshley, gallywix, voljin... you get the point. BGH is used and it targets FAR fewer minions actually played than blackhand rend. And while BGH provides a larger tempo swing, Rend actually has more consistency due to having more targets and in fact will help you save removal for other targets.
As a paladin, when I am facing down a ysera, I have 2 options right now - and sometimes a rare third option. The first 2 options are 1. silence and hope ysera doesn't just plain out value me with her 4/12 body or I can end the game fast, 2. equality. Granted, equality isn't a great option. Sometimes it isn't even an option at all. So both aren't really great solutions to single targets like ysera who can't be BGH'd. Same deal with kelthuzad, although usually equality + consecration/wild pyro is worth it since it clears an entire board and not just 1 minion. The third rare option is having 12 damage on board + kelthuzad to revive everything back.
Next, I just want to point out that the dragon requirement is more of a deck building requirement than a cost requirement. Most of the time as paladin, I'm hoarding resources anyway. So I have a hard time imagining a scenario where a dragon paladin deck lacks a dragon in hand. We'll see though, cause I suppose there will be some situations where I am forced to use dragons or I have played too fast and am top decking. I just don't see the dragon in hand requirement to be much of a downside, if any at all. It is gonna depend on how the deck is built, which I can't say atm since we don't know all the new cards yet.
Lastly, while Rend can be removed fairly easily himself, he demands that removal. There is a lot of pressure to take out an 8 attack minion of course. And I don't see that as a big downside if I just removed one of the cornerstones of your deck while playing a 12 stat minion (about 5 and a half mana worth of stats). If you think about it as a statistic break down, its about 1.5 mana to remove the legendary and 5.5 mana to make a 8/4 minion. So even when it gets swiped, the opponent is spending 4 mana to take out a 5.5 mana minion. If you just removed ysera, you spend 1.5 mana to remove a 9 mana minion. You're ahead, in other words, for total mana spent in the exchange, and your rend black hand just 2-1 against your opponent.
-Long post, but that is my thoughts on Rend Blackhand. I feel like I have been pretty accurate in a lot of my card evaluations in the past. I wanna see how I do with Rend Blackhand, a card a lot of people are dismissing quite easily.