I'm wondering if that 10 am boat is also the one that books cruise ship people onto it. If so, those people are often coming back to Blue Angel for a quick, prearranged lunch--that could explain some schedule limits. When we've done their 8 am boats, no one has ever told us when to get out of the water. We'd be looking for a different operator if they did. Mostly we did dives of about an hour and change by choice, even when we had plenty of air left, and the DMs were good at designing profiles that ended in the shallows. There was one Villablanca Wall night dive where a few of us stayed down for about an hour and a half because it was such a good night dive.
I'll echo the love for Columbia Shallows. Last trip (not BA), we did it after Marracaibo. Aside from looking at the deep ledge and thinking (for the few brief minutes of non-deco time allowed) that it was as pristine as I remember Santa Rosa in the early '90s, I didn't find Marracaibo as purely pleasurable as the colorful, easy, gorgeous diving of Columbia Shallows. I really like Francesca too, just because it's pretty and fishy. I'm not as big a big fan of the northern reefs as some here are, but they get points for being fast and deep, if that's what you like.
As for locks/lockers at the Blue Angel. Maybe someone can offer a sharper memory for this, but I seem to recall bringing a standard combination lock once and finding the bin hinges too small for it. Might be worth checking into if you're looking to lock your stuff up. We always carry our stuff to our rooms anyhow. I think the closest I've ever had to having a locker issue there was leaving a mask box or something in the gear-up area while doing a shore night dive, and someone conscientiously putting it in the lockup for the night to ensure its safekeeping--my glasses were in it.
It is very easy to catch a cab at BA. The only time it's ever even a bit hard is if it's right after a cruise ship has docked, and everything going into town is full.
But, Sideways, I'm thinking I'd rather one of my next dive trips be to the Similans, based in part on your pictures. Got a trip report up anywhere?