Locks that work

Skateboard helmets or nothing in my opinion (for commuters who keep their helmets for a long time and only make shortish journeys).

Soft shell helmets for racers & long distance riders where the weight matters more than durability.

In a traffic crash, if you manage to avoid getting squashed it is highly likely there will be sharp/pointy debris trying to stab your skull. Good quality hard shell helmets can offer a lot of defense from this. Brands like Pro-tec also have multi impact technology.

You can get multi impact roadie helmets, but they are £100+ and still have the vulnerable soft shell.

^ this.

If you really want to protect your noggin', do it properly.

There are very good (and admittedly expensive) helmets that doesn't get hot in the summer like those two;