Holy Jackson H Howard! Such a lack of enthusiasm for this card! Ok, I'm here to tell you that this card is cool. It is a typical case of a card that needs to be played correctly to get the most out of it.
Rules first: Yes, in both cases it's the Corp that gets to decide which card gets rezzed and derezzed. This means they can chose to derez a Jackson Howard. Thay can chose to rez a Curtain Wall.
But as a Runner, you get to chose when this happens. By careful manipulation of the board state, you can make sure that all of the Corporation choices are bad. That's all there is to it.
Let us start with the 1st ability: derezing a card. Because they can derez a Jackson Howard, you obviously don't want to play this when there is a Jackson on board. Duh! Ideally, you want just one card to be rezzed and that card should be expensive. So it's a good idea to play this early on. An ideal play is to face-check into some beefy ETR ice like Lotus Field on turn 1. Bounce off it. Play Muertos. Bam! Corp is poor. You can run that server again. They will need a turn or two to recuperate. Plus, you exposed the ice and know exactly what to prepare for once they get their money back up. Even if the ice is an Eli 1.0, this is basically a 3-credit loss for a click. That is great on turn 1!
It is especially good against Blue Sun: Powering the Future, which will rez expensive ice on their own using Oversight AI. Because of their ability this will often be their only rezzed ice and Muertos will be a direct counter to this.
Moving on to the 2nd ability: trashing Muertos to allow the corp to rez a card. This seems bad. But it's actually not a big deal if everything has been already rezzed. For example, you can keep facechecking aggressively, forcing the corp to rez all of the ice. Once you do that, you can pop Muertos and they won't be able to rez anything. You mitigate the downside and get a cool card draw from this.
Muertos has some neat synergies with a bunch of Criminal cards. Forged Activation Orders allows you to force a corp to rez and ice or trash it. Either way, it eliminates a potential rez target for the 2nd ability, allowing you to pop Muertos for card draw earlier. Leela Patel: Trained Pragmatist likes this as well. Playing Muertos gives targets for her Abilty even late in the game. In return, her ability removes targets for Muertos 2nd ability, allowing you to pop Muertos for card draw earlier once again. Silhouette: Stealth Operative is great at scouting ice. If the only unrezzed ice is cheap, you can safely pop Muertos and be sure it won't give the Corp much of a benefit. Armand "Geist" Walker: Tech Lord gets an additional card draw if you manage to pop it. Finally, they are a connection so you can tutor them when you need them with a Hostage and since they will be hanging around for a while, you might get them to boost your Calling in Favors.
And yes, they are probably a good reason to get drunk on jank one evening and try that Blackguard + Silhouette: Stealth Operative combo that didn't work so well last time around.
Muertos might be even fun out of faction! With Reina Roja: Freedom Fighter the derez has an additional sting. Valencia Estevez: The Angel of Cayambe may be using them to keep servers unrezzed so she can Blackmail into them. Instead of Forged Activation order you can play the under-played Cyber Threat. And of course, you might want to put them on an Off-Campus Apartment so you get even more card draw!
Muertos certainly has a weakness against cheap ice like Pop-up Window, Pup or Quandary. Face-checking into this ice to derez it won't be a significant hindrance for the corp. It difficult to pull it off in terms of influence, but it might be worth thinking about Parasite to eliminate those targets. Another neat card to combine this with would be Social Engineering. If you can spot the expensive ice, this can put the Corp into quite a conundrum. If you want to crank up that jank, you can even play False Echo to eliminate targets for the 2nd ability.
Another weakness of Muertos is that you can't go Tag-me. The corp will be able to play 2 credits to trash your Resources and rez stuff for free. So you want make sure you remove those Account Siphon tags as long as they are out. You might even play it with Fall Guy just to be sure. This would work well with the above mentioned connection plan. Armand would approve.
Anyways, Muertos Gang Member is a cool, complex card. It offers great benefits if you are willing to play a strategic game. So don't put that in your folder yet! Have fun and experiment!