The AT is definitely the more spectacular watch when viewed from the back exposing a great view to the sparkling Caliber 2500. The Grand Seiko offers their traditional Lion logo. Older Grand Seikos from the 60ies and 70ies had an 18 Karat Medallion featuring that Lion on the back. Looks fantastic, because I had the chance to see it on Seiya-san's vintage Grand Seiko. Opening the watches means to have a special Omega opener with round bits or any Jaxa or Bergeon style opener with round bits. The Grand Seiko's back has the normal rectangular notches plus a ring that reminds of Rolex case backs. I have studied the grooves, the look like a decoration only, but are deep enough to act as "teeth" for a special Grand Seiko opener Rolex-style.