Aargh, I just wrote a long post in praise of the IKEA Antilop chair and then lost it in the bustle of getting into my commuter train!
Anyway, I agree that this chair is fab and much more practical than any others we've tried. Both DCs really liked that they could sit up naturally in it - they always seemed slumped in other chairs, or forced into a reclined position that they hated. They seemed to have more freedom of movement, which is great if you're going to do BLW - as is the HUGE, easily-wipeable tray! We did use the inflatable insert, and it was useful when they were really tiny, but we stopped using it well before a year for both if them as they were getting a bit "wedged in". Once your child can sit up confidently, it's not really necessary, no matter how much room.there is around them in the chair, iyswim.
You might find that you can fit the chair under your table with the tray off (we couldn't, as it was too high to go underneath our (also IKEA!) table). We just left the tray on and pushed the whole thing right up to the table so the DCs still felt included in the family meal. Once they were about 1.5 or 2, we moved to a booster seat on a normal chair, anyway, so it wasn't really a problem.
Cowbag, I know what you mean about the harness - and sort of agree with you, actually, as both DCs went through a phase of hanging perilously over the sides. We got round his by using a separate five-point harness (a set of reins from John Lewis - they don't seem to sell them any more but these ones are similar) that we threaded through the slots in the chair. Our chair is about 5 years old, though, and I believe that IKEA introduced new straps on more recent models (and will replace the straps on old chairs free of charge). Has anyone else done this, actually?