Again, I did a search and couldn't find a thread dedicated to just top-bar viewing-windows..................am I wrong?

I am in the process of custom building two hives for a lady and I'm using the general design of Phil Chandler over at biobees.com
for the overall hive.

I saw someone mentioned over at his forums something about locking hinges. Has anyone here used those?

Please post photos of your viewing-windows and a bit of explanation about what works good about it and what doesn't work.

I was thinking about going with this general design. Any pros or cons I should look out for? (This is not my hive)