I have a soft-sided Curtis Cab on my 4310 with a heater and I'm very satisfied with it. I've had no leaks, except that when I'm blowing snow, the wind can blow snow under the front lip of the cab roof, where it melts and drips down on my knees a little. This is just an occasional problem. Rain doesn't come in.
The cab does nothing for sound deadening, and may even amplify it a little bit. I always wear ear protection, unlike my neighbor with a big JD farm tractor with a factory cab. He says his is nice and quiet inside.
Tom