Just as a point of information, the CARES device does not have a TSO-C100b certification. Rather, the manufacturer demonstrated an equivalent level of safety and received approval through 14 CFR 21.305(d), which was the old method for the approval of materials, parts, processes, and appliances.
Also, some seats have recessed table trays, which then requires that the upper strap wrap around the outside of the tray. It's possible that SQ have seats with this configuration?