Another thing is that it doesn't increase the game speed, and can result in defensive play due to higher risk.
I personally like the 2stock5min ruleset for earlier matches and 3/8 for later matches in tournaments and whatnot (especially on the 3DS version where you can easily do Swiss pools), since that lets the "lower" matches go faster while leaving plenty of hype for the big fights. Also, maybe it's just me, but I feel like blast zones are closer on the U version than they were on the 3DS ver (or maybe it was the patch), so that (if it's actually true) will affect match length as well.