You have nothing to worry about with Aer Lingus - it's a nice airline these days and it is more comfortable, IMHO, than Ryanair. That said, for the sake of 50 minutes, I wouldn't stress about it too much.
Of course, BD will give you a free baggage allowance, but they will likely charge you several multiples of the fares you have already seen.
When costing a cheap trip ex-LON, factor in how much it may cost to get to your departure airport.