I've noticed that many of the combo seats that go from the 5 point harness baby seat to a toddler booster seat using the seat belt, have belt positioning clips on the upper sides of the seat.

Should this be something I'm looking for as I research a new seat?

Someone on this board mentioned that the belt positioning clips can cause slack in the seat belt when used in the belt positioning stage. Could anyone tell me if they have found this to be true with, say, the Graco Cargo Seats? Would it better to try and find a seat without the clips? I have not been able to view a Britax Marathon or an Airway Booster seat- how do they convert to the seat-belted booster seat?

TIA
Mkt