There is a propensity for heel strike on the front wheel in slow speed turns, ie within or slightly larger radius than half of 2 lane road. Leg suck with a 26" wheel is relatively unlikely as the distance to the
ground is large enough that most riders would arrest the leg before it hit the ground. Others have
different opinions, but I feel a dual 26" is intended for riders at least 68" tall. Shorter riders can ride
one but have to shift the body forward in the seat or tippy toe to reach the ground.
Not exactly cheap but www.carbent.com has interesting dual 26".