Like to ask the Seiko pros here, I was reading up and looking at the various Tuna. Looking at the Seiko US website, there are a Prospex Master Series and a Prospex series.
The SBDX014 (under the Prospex Master Series) and the SBDX011 (under the Prospex series) have really similar specs and prices so I don't really understand why they are in different lines.
I don't know much about these tunas, but will try to answer based on what I know. SBDX011 has been around for several years, while SBDX014 is quite new in the market.
Similarities:
both use the same 8L35 movement (Its a GS movement btw)
Differences:
Gold color trimmings on SBDX014
SBDX014 uses ceramic shrould which is both good and bad.
Ceramic shroud is
(1) very scratch resistant
(2) Ceramic shroud surface looks very good
(3) BUT may break if dropped accidentally onto hard floors. (You can check out those painful stories of ceramic cases breaking apart, not just this watch. e.g. Omega's dark of the moon watch also uses ceramic)
The hour and minute hands are different. Most pple like the SBDX011 hands better than the new ones.
The date is moved to the 4 O'clock position. You get to see 3 o'clock markers if you are in the dark ocean... but for desk divers, the old 3 o'clock position for date is much easier to read.
More expensive! Duh
In conclusion, if price is not an issue, get the one that is more visually appealing to you. If you get SBDX014, be careful not to drop it!
Oh btw, please try it in person before you get this watch due to the size of this watch. Most recommend 7 inch wrist minimum for this watch but I think 6.75 inch wrist should be OK.