The goalkeeper joined from Chelsea last month and Mertesacker is encouraged by his arrival.
The vastly-experienced goalkeeper was secured from Premier League rivals Chelsea last month in their only move of the summer transfer window so far.
That deal has, though, been met with widespread acclaim, with many believing his arrival at the Emirates has solved one of the Gunners' biggest problems, with it being suggested by many that securing his signature will push Arsene Wenger's men closer to a potential title challenge.
And Mertesacker says he is looking forward to working alongside the club’s latest recruit, with the Czech adding important qualities to the ranks.
“I thought that was a good signing for our team,” he told arsenal.com.
“He’s an experienced goalkeeper who proved that he is a really good ‘keeper and won a lot of titles with Chelsea. I think it’s a great signing for us and from day one, when I first met him, you had that feeling that he has a certain presence.”
Arsenal to see the best of Cech
More than anything, Cech is adding some much needed experience to a relatively young Arsenal side, with the 33-year-old having won just about every major honour while at Stamford Bridge.
It is hoped that he will have a positive impact on Wojciech Szczesny, with Wenger clearly hoping that the Polish goalkeeper can come good in the future and be a regular Arsenal number one.
Mertesacker, though, says that Cech can add that something special to the side in the present and is confident that Arsenal will see the highly-rated shot-stopper 'at his best'.
“He can add that special [something] extra we are missing,” he added.
“That’s why he joined - he needs to regain his confidence by playing for us and I think that’s the most important thing for him. Overall he’s played a lot of games in the Premier League already. He will add a few games and we will see him at his best.”