I have both this koo-di seat and the Baby Polar Gear Booster Seat for my son. No contest - I recommend the Baby Polar Gear (BPG) seat way over and above the koo-di harness seat. I used both for my son last year when he was 18 months old on a trip to NZ and South Korea.
Merits of BPG over the koo-di:
- koo-di did not fit on several types of chairs due to width or height of chair back, BPG didn't fit one chair (those moulded plastic curved seats) as couldn't get the straps around the chair, so I just fed him in the pushchair
- my son sat upright and did not slump in the BPG, which sometimes did happen with the koo-di as it depended on the chair it was on (which you mostly cannot control)
- used the BPG to keep my son stationary on the airplane (see my review on Amazon page for the BPG) - which was frankly AWESOME! Koo-di lacks the structure to do this
- BPG is plastic and wipeable (koo-di you have to wash because it's fabric)
- He's outgrown the koo-di (I've now given it away), but he still fits easily into the BPG, and it looks like it'll last him a good while longer
The koo-di seat does win in terms of volume as it packs down really small, but this is a minor point compared to the others.