After comparing all the stem mount baby bicycle carriers, the Thule won out for its quality and features. The mount is fairly low-profile when the baby seat is removed and it comes off smoothly.
Small to medium sized riders may have contact between the baby seat and their knees (depending upon their bicycle and stem type). I'm 5'9" riding a medium sized, touring frame bicycle. With my saddle adjusted back a bit from my normal, my knees just miss the seat while pedaling.