Info request on difference between see-through and steel case back (Sinn 103 St)

I'd be happy to know case back weight and height differences. (My estimation on height difference is about 0.8 mm, no idea on weight difference.) Thinking of up-grading my 103 St with this.
Other question is that I could put my hands on a domed sapphire glass for this watch, unfortunately outer antireflex layer is a bit scratched. Any idea what the renewing of this layer would cost at Sinn? Going to an optician would be a sound idea for renewing this layer like that of spectacles?
Sinn factory members are also welcome to chime in...
Sorry for posting in English this time.
Thx a lot, best:
Robert