I was thinking about getting a great bascinet for reenactment and maybe 1 on 1 bohurt fights, but I have no first hand experiences with them. How is it to fight in one compared with a normal bascinet? As far as I understand, they sit on your shoulders, right? I would like to take the weight off my head, but I'm sure there must be a catch why these aren't more popular for full contact fighting. Do you need a collar underneath it or is gambeson, coat of plates and padded hood enough?
Thanks in advance for your answers. :)

Certain designs of great bascinets make it hard to impossible to turn your head and the helmet. Ian la spina made a video about this. The additional protection for the throat great for jousting and calvary combat but bad for foot combat because you can't have your head on a swivel.

Yep, that doesn't sound very good. I was thinking that you could move your helmet left and right inside your helmet, but you would need longer eye slit to the side to be able to exploit that... I don't know how well that would go...

well for your intenon is reenactment and "bohurt" fighing the disadvantages which made it not perfectly suitable for real footcombat do not really count.. since i participated in the grunwald 2010 reenactment where a guy in a great bascinet kicked ass i've seen many of seem in bohurt tournamnets and they can be excellent helmets depending on the role you play in your team

This is just another one of those pieces of armour that have to be made right, by someone who actually understands them, and most modern smiths don't get it. Yes, they rest on the shoulders (not too wide, now!) and are fastened down front and back, but if the helm is so small you can't turn your head inside it, it's too small for you. The face openings, with the visor up, are enormously wide, and the openings in the visor reflect that, so you can take a diagonal stance and still see out of the thing. They were enormously popular for foot combat for quite awhile, and used quite a bit in battle by men-at-arms in the first half of the 15th century.