The Spree line is KZ's highest level of equipment. There has not been many issues with them and I would not have a problem looking at them. Personally I think the fresh tank size is kind of small, but we camp at a lot of electric only parks.
As far as towing goes, a 8x10x32' box tows differently than the other types you listed. It has more frontal area which takes a lot more power to pull through the air at 65mph and the 10x32' side profile is more susceptible to any wind that is not directly in front of or behind you. Your towing experience will help you but very few people tow a high walled RV like there is nothing back there. You always know it. I'll assume you have a 3/4+ ton vehicle. Get a good WDH with integrated sway control.