You're welcome... but I wouldn't go so far as to consider your purchase useless. My son spent two seasons in his bike seat before graduating to a Trail-a-Bike. You might be able to find a cheap, used rigid (non-suspended) MTB in your area that would make a great platform for the child seat. I did just that, gave it a tune-up, added a set of riser bars and some slick tires, and presto... family commuter!
I didn't find that using the bike seat affected my balance too much, although I was aware of a difference. I noticed a bigger difference in wind resistance; the seat back there acted like a little parachute. Nothing I couldn't overcome, but it was very noticeable when riding into a headwind.
