Clotus-
I have read that the Dometic 310 is not user-serviceable;
see this thread on iRV2. It sounds like a "disposable" toilet. I could be incorrect.
If I were making this decision, I'd be inclined to stick with a Thetford model, and hopefully one that is compatible with the floor mount and water connection of my existing toilet. I had a Thetford Aqua Magic Style II in my coach. Except for having to replace a leaking valve twice in six years it didn't give me any problems.
If you do switch to a Dometic, make sure understand any required floor mount modifications before you buy the toilet.