I worded myself poorly. Yes, it is auto-adjusted from the spring-loaded tensioner arms, but you can't manually adjust it to add more tension in cases where the belt is loose. Ideally, and in the majority of situations, you never need to. That all said, it's not something I've personally dealt...
I would absolutely recommend going with a Zero Turn. The speed, comfort, and maneuverability difference is night and day. I definitely agree with your initial choices of Gravely XL or the Raptor XD. Another you could consider is the Bad Boy ZT Elite, which offers commercial-tier components at...
I have been looking at zero turns for about a month now and a ZT HD 52" with the Kawasaki engine was in my top 3 finalists. I really liked that it comes with commercial-grade serviceable transmissions and strong engine options which are more than enough for residential use. Heck, 10 years ago...