Additional risk factors I've witnessed with certain low-cost carriers:
1) Infamous warp-speed taying to make block times - how on earth are they ever gonna stop if something gets in the way?
2) With 15 minute turnarround time, what safety checks do the crew get to make? Surely there is increased risk of missing something glaringly obvious.
3) Extra long crewing hours (this applies to all airlines these days, but I think it fair to say more so to lo-co) - how well will they perform with the emergency on the 6th sector of the day having just worked 13 hours? With unrealistic schedules, any problems during the preceding sectors can easily increase the duty day beyond planning maxima.
A quick look at CHIRP shows what the flight crew think of this abuse of the rostering (look at almost any issue and you will find some talk if this abuse. This is really a failing of the regulator, which is abused by the airlines.
4) Perhaps someone in the know can explain this, but they are (nearly) always ready for departure as soon as they get the runway, not matter how quickly that happens. Do they not do a (full) safety presentation? When the crash does happen for whatever reason, how well prepared will the passengers and cabin crew be to exit expeditiously?
5) You pay peanuts, you get monkeys. Some of the rates paid by the low costs for stafflower down the food-chian, who are still vital to the safety of the airline are unbelievable. These peole are not staying to gain any level of expertise, and must be quite demoralised. Safety can be compromised to some extent by all sorts of the ground staff from ops, dispach, baggage handling etc.
Low cost airlines are still quite safe to fly (otherwise they would not be allowed). Accidents probably cost more than safety, and if you are after profits you will bear that in mind. I can not be convinced, however, that they are as safe as the old dinasour airlines with full checks, whole career's worth of experience and better motivated staff(?)
[ramble off]