We have recently bought the seat size 3 for our son, who can not sit alone because of a tetraspastics. We use the Sitter Seat for traveling, as a guest and traveling. So we do not need a big, heavy, carry unwieldy therapy chair. After repeated use, we are still very satisfied with the Sitter Seat. The handling is simple (Seat is simply fixed on an armchair with 2 straps. The seat is light and easy to transport (a pity that it is not allowed in Germany as a car seat, then you could save even more luggage while traveling!). The birth is also very good. So a clear recommendation! And now I would like to take him to the next cinema, so that we can all watch the movie very relaxed;)