It was definitely easier than 10 man normals are now. Nobody is asking for LFR level, that already exists, but a setting where you still do things like make assignments and ahve jobs to do, but aren't punished for bringing Bob the Builder, your best friend...that's good.
Also, it works just like it sounds, you can't queue for it, so you're not FORCED into bringing anything, but it's not like you're just making a raid of 0 tanks 2 healers and 12 dps and going to succeed. It's almost assuredly expected that you have 2 tanks, and that you have a proportion of healing that can handle the content. My guess? If it were real raiders you could probably like 3 or 4 heal a 25 man flex raid, but you'll probably just bring whatever you can muster since it's just for funsies.