>>418673610
Actually that's a super common question and the secret is that the WHOLE eye hole is a mesh you can see through, the field of view is obviously hindered but it's not nearly like what you'd expect these days, you take FoV into account when making the head base before furring it. 
The heat is definitely an issue you're right but most people wear cooler vests, have in-head cooling fans or spritzers and many people turn little accessories into fans that you can hold to the mouth of the head for a quick boost of cool air, so it works out :)