I can give you my personal experience since my tank is Rimless and started out with no canopy and now I wouldn't have it any other way. I do love a nice take that is rimless and has a nice light set up that makes it look like they are suspended in mid air. I had Radion Pros and hated the RMS arms because it causes the lights to sag and having had 3 over the tank I was very particular about them all hanging at the same height. Then you have to worry about your tank mates jumping out, I have multiple wrasses and was stubborn and had many carpet surf so going without something on top was not an option. Sure you can run the DIY screens.. but that ruins the look of a rimless tank. So that was a NO GO. So I broke down and built a Canopy that would allow me to get into the tank. Like the OP said, it can be a pain in the neck to do maintenance if not set up right. Then as another person stated they don't like the light leakage that happens with a rimless tank.
When I made my Canopy it flips up on the front and one set of my T5's and Reefbrite XHO LED bar also flips up with it. So my lights are out of the way in the front, and leaves plenty of room to get into the tank when needed. Or I can open one set of doors on the front for feeding time, and with the soft close hinges I don't have to worry about the doors slapping the Canopy and scaring the fish and making them jumpy.
If I had to do it all over again... when I upgrade, I will be running another canopy.