My opinion absolutely not. One of the most forged autographs in the hobby. Some forgeries are very very good this one isn't.
Here's a good site to compare also when I get a chance if needed I'll upload a pic. of my in person Mantle for comparison.
Yikes.. Without a higher resolution scan it's impossible to tell if the signature is fluid or if it stutters in the loop of the M, to me that would be a big red flag. Unless Mike Frost knows something about it that I don't he took a big risk passing it. I don't like the way he does business, but if his opinion is good enough for you than go for it.
If PAAS actually said this was real it wouldn't surprise me. lol However on an on line examination I've never known PAAS to say definative if it was real or not. If you did indeed get an on line examination by PAAS I'm sure you wouldn't mind copying and pasting the email you received from them here. Like tansk1 said "if his opinion is good enough for you than go for it". Whatever makes you sleep well at night.
.
Never argue with an idiot. They drag you down to their level and beat you with experience.
Likely to be genuine: Our authenticators believe that the item, if physically submitted to P.A.A.S. for examination, would likely receive our certificate of authenticity.
* Please note that this on-line examination is based solely upon a scan.
Thank you for your trust in P.A.A.S.
Michael Frost.