jimc101

First consideration should be fit, regardless of your budget, all helmets fit heads differently, you need to try them on to find what fits your head best.

For other factors you have listed, ventilation, does it matter if you are buying now, as for the next 6 months you will be riding with a skull cap or similar, it's too cold to ride any real distance in the UK now without something warm under the helmet.

Protection / durability, Durability in use, the more plasitc they have covering the polystyrene, the better, for crashes durability is not an issue, helmets are single use items when it comes to them, for protection, they all have to pass EN standards, so none will be significantly better than any other, or a £9.99 one from Llidl / Aldi.

Weight, you have coved this.

Another thing to look at, crash replacement policy, Giro and Specialized have good ones, claimed on Giros several times myself, for the others no experience with those brands.