What's the differences between the Mantilla respirator, Sarum-Pattern, and the Heresy-Pattern helmets?

https://preview.redd.it/fb0iz62qjrke1.jpg?width=415&format=pjpg&auto=webp&s=5def67889d90285431e6e7a73cd117e09ab4c9a6

https://preview.redd.it/52arfc9qjrke1.png?width=372&format=png&auto=webp&s=1df115a84a2632fe7b4105965c510676b79970fe

https://preview.redd.it/kqn99c2qjrke1.jpg?width=529&format=pjpg&auto=webp&s=b049a5774734b580aaa8833478e9593c82e3a07b

I get that the Mk.5 has the bonding studs, this properly made from inferior materials, but what's the actual differences between these helmets?