Thank you for all your great advices! I read them with great attention. They confirms what I'v read about the UForce 800.
But last Friday, I went to the closest dealer near where I live, a half-hour drive. The dealers was closing earlier than usual due to a special circumstance and we only could try it for 5 minutes. It was a U 500 instead of a 800. And my experience was not on par with what I have read until then: the responsiveness of the gaz pedal was very slow and there was this big vibration coming under our bottoms, so big that i supposed it would get us numb if sitting on it for more than 10 minutes. A bad experience far away from what I have read on this site and on other sites. So I supposed that it was a problem specific with this machine and I'll go check another dealer who has the U800 to see if the experience is better, as I expect.
Because we had time, we went to the Polaris dealer close to the CFMoto dealer. And we tried the Ranger 570 and liked it a lot. No vibration, responsiveness of gaz and good dealer. Less equipped, but the price is not that very different from the U800 if you take only the winch, roof and half-windshield and power steering.
I'll go try the U800 and report here after.
Thank you for your great advices