There's a mom in my Moms Club who has a Sit N Stand and she LOVES it. Her guys are 4 and 2. She said that the only problem is that the older one has to be a good listener. There is a "seatbelt" but it's not really a good way to restrain them. So if the oldest wants to take off, there is really no stopping them.... Which is why we haven't bought one yet. Alex would rather run than sit and I need a good method of containment for him.
But everyone who has bit the bullet and bought one though seems happy!