I have two questions.

I have an sd card that worked perfectly in a Note 3, class 10 etc. In the S7 it seems to have a lot of problems being read at times and can be very slow.
Is this a phone issue or the card?
(still works perfectly in note 3)

Are there any recommendations for a case for the S7? I am looking at the
http://www.ebay.com.au/itm/Slim-Armor-Bumper-Heavy-Duty-Case-Cover-for-Samsung-Galaxy-S6-S7-edge-Note-5-/401051111373?var=&hash=item5d60824fcd:m:mtdvBqIttm0w2QZbY-1gR6A

Lastly, I know I said two questions, do the screen protectors only protect from fingerprints, scratches etc or do they also reduce the chance of the screen cracking if you drop the phone.

Thanks