Ok, I know I'm going like I'm picking on you with this and all..though honestly, these shield ideas are poorly thought out. Here's why:

1) You haven't explained what their bullets would be like.

2) Then wooden shield doesn't seem all that useful. Toaster isn't that great of a weapon. It's mainly used as a last resort, and to camp exit passages. Or, if you have no other weapons, or other powered weapons for that matter. If it only protects you from toaster, I could only see this shield being utilised in a level with only toaster pickups/the only PU being toaster, utilising unfreezing springs, with sparingly placed ice pickups. And how does wood protect from fire?

3) Utilising the Metal shield would require a layout that's more vertical and diagonally based, because RF is very strong in horizontal passages. Seeker pickups would be fairly common, I guess.

I could see these two ideas working in a one-time scripted level with some more thought. I believe the new shield should be versatile when it comes to making use of it, when creating a level.

4) On the other hand, the clay shield idea is worst idea so far, because it's no fun to be immobile. Not only that, the enemy can just sit beside you and wait to hit you until it wears out. Even if you could shoot, people could easily stay away from you.

Where I may be going wrong, is that I don't exactly know if the wooden and metal shields protect you from other types of shots in a way like the regular shields do. If they don't, then they truly are super situational and my points stand out further. I got this assumption because you mention the wooden shield protecting from getting hurt by toaster shots, which all other shields can do.

Maybe if the ideas weren't half-baked, I'd get a better idea of their potential, and would maybe delete this post.