We are also considering the Curtis Cab and have been told the same thing about the heat. However, if you have the doors open and the flap down in the back you have a lot of air flow. You can also open the front window and screens are available if you are not fond of picking bugs out from between your teeth...
There is also a bit of a "closed in" feel as opposed to the totally open feel without it. On the other hand, letting them dry and having to roll up those flaps is a bit of a pain in the ash, it seems to me... On the third hand, how often do you need the flaps down, or the doors closed? Not having owned one that's hard for me to say. Perhaps someone else can address that question.
The doors go on Yamaha, EZ Go, and Club car. Club car has the most colors available.
The weight may be a bit of a factor, but we have not noticed any difference on test drives. Perhaps an electric cart (one with poor range) would not be the best candidate for a Curtis Cab due to the added weight (I have been told up to 180 pounds).
There is also a bit of vision obstruction (some more than others depending on the model), but I think I could get used to that... some dealers will install the heater / fan that Curtis Cab makes. You can "google" Curtis Cab for thier webiste for more info.
The cost seems to vary from about $1,700 to $2,400. You can check them out with the local dealers.
One other consideration... it's easy enough to get to your golf clubs with the cab, but the sand bottle is a bit more difficult... though not impossible. Finally, the cooler will not fit on the Club Car with a Curtis Cab on it, but you can always put a cooler in the basket.
We continue to go back and forth with the idea... Decisions, decisions!