I had one in a 55 that disappeared in about a week. No idea what happened to it. It did lay eggs right before it disappeared. About 3 months later, when I took down my 55 to transition to my 120, I found a baby nudi on the glass that somehow survived. I was amazed. I haven't seen him since though in my 120 but if he hangs in the rocks, I am sure he is there somewhere.
Anyway, back to your question, I got mine mail-ordered and he looked fine but I had tons of flow in the tank and it looked like he would be blown away any minute sometimes. My guess is he got shreaded up in my maxijet. So, if you guard against that stuff, I don't think they are any different than anything else. They do a pretty decent job on HA but a sea hare does better.