Essential winter clothing?

I was looking at getting one of the endura insulated gilets. You’d recommend? And how do they size up (endura sizing always seems a bit random)?

It's a great thing to have & I've started to carry it with me for all winter rides for long stops/emergencies. The two way zip makes it pretty versatile, I'll wear this over a jacket in deep winter (sub-zero) but also over a summer jersey in spring/autumn. Fit wise, I'm Small in most brands and this is no different.