We've flown with them a number of times, and not had a problem that I remember. Although looking at my accounts I can see back in 2008 I was charged for a flight 22 hours after attempted to book it, and it was refunded a day later, can't remember the details though.
The planes are no different to any others, don't all airlines like to fill theirs seats, thus they all become crowded? I'm six foot and had enough room on our last flight with them.
What you have to watch is your baggage options, easy to get caught out. We last flew with them in January from Stanstead, paid extra for priority boarding, and fast track security, which was worth the extra. We didn't know at the time so we queued at check in expecting them to put labels on our cabin luggage as per our last flight (which was to Canada), turned out we could just walk straight through to security, where we had to ask where fast track security was and then we walked past every one else :-)
Also make sure you do online check in and have your boarding pass either printed or on your phone, I do both.
I'd happily use them again, especially if it saves me some money