For the average size American adult, the CH640 is more like a 2+2 than a true four place. Even with the lowered floor and extended rear seat options, there won't be much legroom for back seat passengers. The CH640 is actually derived from the part 23 certified 2 place CH2000/Alarus trainer.
Otherwise, there's nothing wrong with it except some people may have difficulty getting into and out of the back seats. Personally, I'm a Zenith fanboy.
Photo from the Zenith CH640 website:
![]()