SEN's weather is generally pretty good, again no worse than STN. It quite often benefits from things going tits up at LCY.
What makes me think it would last from Derry? Well, there wouldn't be any other option primarily. I think the Stobart fare structure would offer cheaper fares in greater numbers and help stimulate the market. I'm confident that if the good people of Derry had to use SEN, they would be highly satisfied after trying it.
I have the benefit of living equidistance from SEN and STN. Although where the option exists SEN is my preference as a traveller, I'm not particularly pro one over the other. But where I see factual inaccuracies I'll step in.