Yes short cage minimises debris stuck in rear transmission. Reduced to same level of problem as my mountain bike. Solves cleareence issue with 2 inch wide big apple tyres catching rear mech.
Yes chain tensioner keeps chain on when folding 99% of the time.
I realise not all disraillered# birdies may have issues with rear mechs catching wide tyres.

# keeping up snafus tradition of mispelling this word.