Hello, you can view through the dash cam screen. But no wifi or 4G can be used 

Hello, yes. The rear camera is waterproof. You can install it outside. 

Hello, no problem. It can install inside the car and look outside. There is a 3m sticker for you to attach it to the windshield. 

Please check sub-table 2 for the operators corresponding to different countries, please update the operation according to your site. For example Germany is: T-Mobile, Vodafone, E-Plus E-+ Mobilfunk 

1.I’m sure it’s glass - when I clean mine with isopropyl alcohol they make that ‘squeaky’ noise you get with glass rather than plastic, and they’re more resistant to scratches than most plastics are. According to manufacturer website K & F use German optical quality glass so I’m sure they would have been called out for that a while ago if it wasn’t true 2.I drop one last year and it broke like glass ..I’ve found them easy to clean and well made. 3.Looks and sounds like glass to me 4.HD optical glass 5.As far as I can tell it is glass. Excellent optical qualities