Our mattress was starting to feel a little too stiff to us, so we wanted some kind of cushion. It has definitely made the bed more comfortable. Any more than 3" would have been too much. It is a little too hot for both of us but especially my husband, though I hadn't seen any previous reviews saying it was hot. It is summer so maybe that will be ok in the winter. It completely unfolded within 24 hrs and is the exact right size for  the bed (I'm not sure what other people's issues were). For the price, it is definitely worth it.