I get what these do and are a step better than doing the bag yourself. However, after reading the horror stories of a 9.8 book being cracked open, handled, signed, then regraded at a lower value due to being damaged by the "handlers", I would crack the case myself, hard encase the book into a hard sleeve with the sign window open to the signer (with a nice little flap to go over the front of the book when finished).
No one loves your baby like you do, so go above and beyond, create engineering controls yourself to minimize the risks.