Exception No. 1: If RMC, IMC, EMT, Type MC, or steel armored Type AC cables meeting the requirements of 250.118 and metal outlet and junction boxes are installed for the portion of the branch circuit between the branchcircuit overcurrent device and the first outlet, it shall be permitted to install an outlet branch-circuit type AFCI at the first outlet to provide protection for the remaining portion of the branch circuit.
Backdoor conformance with 210.12 (A) ex 1 would be to install one of these Leviton devices in a 4Sq adjacent to the panel, with a compliant wiring method from the panel to the 4Sq. Now, compare the $$$ of the 'device' and an AFCI CB.
I think it only makes sense for rehab or renovation in a house that has a pre AFCI style panel that you don't want to replace. (Zinsco or something) I am surprised these are not dead front. If you are just putting in a few circuits that need to be AFCI, this makes a lot of sense. I imagine you could get 2 in a deep 4x4 or 4 11/16 box. That might be enough for a small addition or a basement remodel. Prior to this you were running a feeder to a new style sub panel that you could buy AFCI breakers for.