Well when he put it like that... Merlin frowned, he was not some kid that needed watching all the time. But he knew refusing would be widening the gap between them, giving Arthur less reason to trust him. Doing this would show Merlin had nothing to hide, no reason why they shouldn't be linked.

And really there wasn't. His face was shadowed with sadness at the comment about not having his magic. It was true... he was completely useless without his magic, he wouldn't be able to protect Arthur if anything happened... But perhaps his weapon could even if it were a book and therefore not all that useful...

"No we can get the link charm first... It's probably for the best." No comment about Arthur protecting him, because Merlin will be protecting him right back.