Do you actually need one? Have you checked your car seat straps are set at the correct height and not causing your child discomfort. Are harness straps suitable tight? They may need to be pulled tighter or made slightly looser. Check with your car seat installer or manufacture to see how tight the harness should be. In most cases you should be able to still just slip your fingers under the tightend harness. Have you spoken with your child and told them how important it is for them to keep their arms with in their restraints?. Perhaps offer them a reward if they complete a car seat ride without removing their arms.
Has the chest clip been tested to the AS/NZS Standard 8005:2013? These standards have been written to ensure that aftermarket chest clips are as safe as they can possibly be when added to Australian and New Zealand car seats.
Please note: Imported Chest Clips that do not meet this thorough Australian and New Zealand standard should never ever be used on AS/NZS 1754 standards certified car seats, as they can not be proven to be safe in an emergency situation or car accident. Foreign standards are not stringent as the AS/NZS 8005:2013 standard and this may mean they may not perform certain important acts in an accident or emergency, like breaking apart, allowing the child to be removed unhindered from their harness restraint.
Has the chest clip been tested on your car seat type? Has it been tested in both rear and forward facing positions? The Houdini Stop had been tested in Both Forward & Rear facing situations and on Type B, A1, A2 and A4 seats. The dynamics on all these seats are all different and what suits on seat type and position, may not suit another one.
Is the chest clip labelled with instructions on how to install & remove the chest clip.? It is very import and part if the AS/NZS standards requirement to label chest clips. This is so in an emergency situation, first responders who have never seen a chest clip, can learn how to safe remove the chest clip and free be able the child from their restraint
Please note, once your child stops removing it arms from the Car Seat harness, you should also stop using a chest clip.