Well... the only experience I have with them is through the military and the historical reenactment community. That being said, the ones I've dealt with were all made of heavy canvas. They do take more effort to set up than the more modern tents people buy today. They are also heavier. The bigger you get the longer it takes to set up and the heavier.
They are sturdier - IMHO - than the more modern light weight ones. These suckers were designed to withstand the harshest environments for the longhaul. They CAN be hot since the material is thicker, but most are designed so flaps can be opened or sides rolled up. They also hold the heat better than most in cold weather. They are also roomier for the most part. When it comes to rain... they are better - IMHO - at keeping it out more so than modern ones. One other drawback, especially if you are not use to one and it rains - neither come with canvas flooring, but modern manufacturers of these do offer them as an extra.
However - I have been in modern, floored tents that got absolutely saturated as well and it's a big PITA to dry them out!
They are also designed more for staying put at a location for a few days - just one night would be a pain.
So, the only difference between a traditional wall tent, and a Sibley bell tent is the shape, and in many cases, the placement of a stove heater.
There is one other option you might want to consider, but I'm not sure if you'll find a bell tent - a vintage, walled camping tent from the '60s and '70s. They are typically made of the same material, but a slightly lighter version, and the poles are lighter. They were designed with weekend family camping in mind. These typically come with a built in floor.
I was fortunate enough to find a vintage, near mint, Coleman 3-room canvas 'cabin' tent a couple years ago to give you an example.