There's no reason I can't hook one on to my kitchen island, right? We currently have a Fisher Price deluxe booster on a wooden stool for DD2, but we bought new stools that are not high chair compatible. I'd rather not buy a free standing high chair.
Little babies don't need high chairs anyway... But a kitchen island seems like the best place to use a hook-on chair! No risk of it tipping over, yk? I can't use those with my dining table; it's a pedestal, and not stable enough.
The only things I can think of are to be sure your countertop is strong enough (does it need/have brackets or is there a seam that could break and be dangerous) and is the overhang deep enough for the seat to attach safely. Ours isn't quite deep enough for the seat, which requires almost 18" and our overhang is close to 15 - we just hook her in the table. That said, I would never buy anything else again. I LOVE our hook on seat.
Re: hook on high chair question