I have two divided 5 gallons, both currently cycled with homemade dividers. One i have had for coming up on three years(its been broken down and cleaned/moved a couple of times but was one of my very first divided tanks)and the other I bought and set up earlier this year.
I personally find that my fish have plenty of space to swim about and do their adorable little fishy things. I've never had any issues at all with someone getting over or through the divider in either tank, even with all the fish I've kept over the years in the first one, and everyones always seemed to be happy and healthy.
I do one partial water change per week, roughly 30-40% or so. When I first set up my first one, I had a little trouble fitting the siphon in the sections, but after picking up a smaller siphon and getting a little creative with hooking it up to my python I haven't had any trouble cleaning it.
Heres a quick picture I snapped this morning:
Don't mind the random explosion of stuff in the middle xD.....I'm also planning on redoing both these tanks with sand within the next week or two.
Anywho, I think I got to all your questions.....? xD Its a little early in the morning for me, I apologize if I missed something.
But overall, I've had great experiences and luck with my divided 5 gallons and I've never had a fish that had trouble with them....though like with any divided tank, it doesn't always work best for every keeper or fish, so it all depends really.