According to page 32 of the Rules Reference under:

USES (X “TYPE”) When a card with this keyword enters play, place X all-purpose counters from the token pool on the card. The word following the value establishes and identifies the type of uses the card holds. Each card with this keyword also has an ability that references the type of use established by the keyword as part of the cost. After the last all-purpose counter is removed from a card with uses (and the effect resolves), discard that card.

First of all, remember that an "Interrupt" ability is not a "Forced Interrupt" ability. That being said, it might as well be a Forced Interrupt because a 1/1 ally with 3 health would be one of the worst allies in the game. If you are playing Dust, I think you are relying on ways to buff her attack like Attack Training, Sidearm, and Boot Camp. In multiplayer, or with Cyclops, things like Inspired and Danger Room Training come into play as well. With enough buffs, and in a multiplayer game with lots of minions, she can be a powerhouse. That requires a lot of work, however, so in an average deck you are best using a different ally. I do enjoy though when new cards have a situational yet powerful effect instead of new cards constantly power creeping old cards out of the game.

Blindfold is an interesting ally that is quite good in X-men decks and fringe playable elsewhere. Thanks to the X-men support cards like Utopia and Danger Room, the bar is quite low for any X-men ally to make the cut in a dedicated X-men deck. Her ability is hard to quantify relative to other game actions but clearly powerful. You need to be mindful of what encounter cards will be drawn as boosts or as encounter cards, and how that changes when you remove a card, but it is a good way to delete a devastating boost effect or a card like Shadow of the Past. It can also help you decide whether you should enter the villain phase in alter ego or hero form, and whether you should tank or block the villain's attack. For example, if you are 3 threat away from completing the main scheme, but you know the villain's activation will only put 2 threat on, you can safely end your turn in alter-ego to get the extra hand size. On the other hand, you could be sure to end in hero form if you know a scheme would lose you the game. One thing I like is you can get all the value out of Blindfold in one turn cycle with a play-activate-block and clear up the ally slot right away, or you can put a Mission Training on and get lots of value over time. Shout-out to Wiccan as well, who always likes to know what's on top of the deck. Blindfold is an easy inclusion for any X-men deck, and with such a unique ability could be a role-player when fighting certain scenarios.

As of Red Skull's release, I think this was a top-3 non-ally Leadership card, alongside Make the Call and Rapid Response.

"Would you play a 1-cost ally that had no abilities, and could simply block once then go away?" "Would you play Invulnerability if it cost 1?" In Heroic? Yes, and yes.

Compared to other 4-cost allies like Martyr, Luke Cage, and Iron Fist, Rockslide doesn't impress me at face value. He plays worse with Med Team than the 2-ATK, 1 consequential damage allies, making him a worse long-game ally, but you don't want to block with him too early either, making him worse than the 2-cost play-activate-block allies. Where Rockslide shines is when you can make use of his X-Men trait. He wears a Protective Training very well, as the bump up to an odd health value gives him 2 extra 3-power attacks. And Rockslide is one of the best combo pieces with Mutant Protection, especially when used on a minion attack. I think you will always play Rockslide in your protection decks that care about the X-Men trait, but I am doubtful he will be too useful outside of that compared to the many great allies already in the game.