One problem I forsee with a MTB R20 is the quality of the 20" suspension fork, most are from inferior "kids"
el cheapo bikes so they wouldn't last long or have much suspension travel on rugged single track. There may be good quality forks available but they would be very costly, there's probably a better choice in 24".

Another problem I could see is the hinge and/or the bolt on the folding frame might not be strong enough for the MTBing that I normally do, so I would suggest using the non folding version frame instead.