Product review (4 stars): Size is perfect for small 2 year old daughter, not as great for 3 1/2 year old son
This has worked perfectly for my (small) 2 year old daughter.  I usually keep it in the car so that it's accessible when we're out and about.  It's small enough to stick in the bottom of the stroller and light enough that it's not a hassle to carry it to a playground.  The only problem with the size is that it's really too small for my 3 1/2 year old son to use, other than a dire emergency.  He pretty much refuses to sit on it.  Since I bought it primarily for my daughter, though, I'm still very happy with the purchase.