Martin is still amazed they managed to sign the goalkeeper from Arsenal.
"He's massive. I think I'm surprised he's here still and that we were able to get him. I'm really grateful that we did," said Martin.
"The support that was shown by everyone to get him. And it took a long time to woo him, court him and try to persuade him to come.
"But he did, and I hope he's getting as much from it as we are from him because there's a character to him which is immense.
"He has a good voice, trains properly, and adds value in a really nice way. Then on the pitch, his saves against Everton were amazing.
"The one from Michael Keane, the top, top save, which we knew he would give us moments like that and that can be the difference."
Martin added: "But also the pressure he takes with the ball. At Man City last week, he did incredible things. Against Everton, some brilliant things.
"For me, he's a complete goalkeeper that we're really lucky to have and we have to enjoy it. He has such high standards and I'm pleased for him.
"He keeps a clean sheet and I think he has an appreciation of what we're trying to be. He's just desperate to help us and he has done."