since I took my 5712.
The 2 reasons why I didn't take the 5726 grey dial was that it was thicker and I perfer the look of the thinner Nautiluses (5711/5712) compared to the thicker references (5726/5980/5990). A matter of taste only.
And that I already jumped from the 5711's budget to the 5712's, so additional budget was an issue, regardless of the AC complication and dial layout I prefered.
Every now and then I look at it with envy, 2nd place behind my 5712.
The AC complication is great (complicated and usefull), I like the dial a lot, symetrical, balanced... and I like the date where it is (even if I think I would have prefered a subdial with date hand at 6 instead but this would have removed the 24h display as well).
The only thing is that I still don't know which one I would pick if I had too: grey or white...
About your 2 questions:
- The stop-second (or hacking display), stops the balance wheel in the majority of the watches you find it in by blocking the gear train or the balance wheel itself. Thus, it is quite brutal (reliability issue) and when you activate your watch again the balance wheel makes several tens of seconds to reach its normal pace. Thus, the accuracy you gain while setting the watch is partly lost when the movment beats again.
So every stop second is not the best thing to have but only the one giving an impulse when engaging the crown again (like in the 5170 and 5235 for instance if I remember well).
- About the clasp: my 5712 works perfectly i.e. it is not hard at all to open. I imagine it can be set more or less tight at the manufacture but I think there may also be a correct way to open it. Personally, I open the part with the securing clasp with my thumb+index, making a leverage effect against my wrist. For the other part, I put my index between the bracelet and the clasp, rotate a little and it opens directly. hard to explain without image

By the way, it it is too loose, it may open each time your hand makes a shock.
I'm sure the latter won't be an issue.
I hope these elements will help you make your own opinion, it's a great project!
Cheers, Mark
One of Oliver's pictures: