They're commonly called Bell Tents and I used them all the time when I was with the local reserves. They are very warm yet somehow cool in the summer. But don't plan on being in your house warm.
During spring and fall, you definetly needed something for heat. Even on some of those cool nights during the summer you needed a heatsource. We used the old Coleman lanterns that ran on white gas. Naptha if I remember right. We also used the Arctic Sleeping bags rated for -40 and then opened the zipper to control the heat.
As for the set up, expect more than 15 minutes. We used them quite often and still took about half an hour to fully set up. Yes, you can get it standing in 15 minutes but you're not moving kit in for at least half an hour to an hour if you want it done right. You spread it out in a circle. Stake the outside corners. Raise the centre pole while a person or two strings the support wires. Once that's done you finish staking the outside edge, finish the rest of the support wires (staked into the ground) and then start tighting them up with the slides that are provided. Then you put logs or rocks or snow on the outside flaps connected to the walls to prevent any wind from getting in. That's about it.
The one problem I always had was standing up in them. I'm 6 feet tall and could only stand in the very centre of the tent. But the problem is, that's where the pole is so I spent most of the time in the tent on my knees or hunched over. If you just plan on sleeping in there, it's great, but for anything else, it sucks.
We had one winter exercise where we spent about 12 hours out of the day in the tent and my back was sore for a week. Try cooking and dressing and working on equipment hunched over.
All in all, it's a good piece of kit. With a little practice they can be set up by just two people in under an hour and if done properly they can stand some pretty wicked weather and cold. Don't get it too warm inside though. Condensation is the enemy! Often body heat is enough or the heat from a small lantern.
400 dollars seems a bit much. Try doing some searching for a Canadian Bell tent and see what comes up.
Best of luck. If you find a nice one and learn to use it properly, you'll be very comfy.