help with buying a 312 please..

[Shrinkdial]

Hi there
I am fairly new to the forum here.
I am looking to buy my first Panerai, a PAM 312- and have a few options.
A seller I am familiar with has a 2010 model, or retail new product (2011 model), or ebay seller new item (2011 model).

The seller on ebay is "jewelersontime" which has 700+ sales and 100% positive feedback.

Can anyone tell me if there are important differences between the M or N series?

Can anyone vouch for the ebay seller?

Otherwise the new watch from the bay seller is only $500 more than the used one from good seller.

Any help greatly appreciated.
Jeremy