I have two tanks running right now. The one with the glass lid is a 8 gallon pico. The tank is rimless and the glass lid sits on plastic clips and there is about a half of a centimeter gap around all edges of the lid (in the areas where there are no clips). The lid also has a hole in the center that's about 2 cm in diameter. The back of the aio tank is open and gas exchange happens there without issues. The tank is low tech-- there is a heater and a return pump (a Sicce 1.0). The return is on a spinning mechanism and provides all the flow for the tank. I have no issues with overheating, but I do run ac in the summer.
My second tank has a hard plastic lid (it's a fluvial flex) that I have modified to take a kessil a360we. That lid covers the whole tank, including the back compartments. I've found that in this tank, I have MAJOR gas exchange issues. I was having random problems all the time and added an airstone to the tank and the problems were solved practically overnight. I do have overheating issues in this tank. I run a heater, a return pump, a mp10 and a 5w uv sterilizer. If my house is over 75 for any length of time the tank temp swings up. I have a suitable chiller for the tank but I really don't want to deal with running a chiller.