The most exciting phrase that heralds a new discovery is not "eureka!" but "holy shit!"
311 karma · joined March 28, 2021
Source: me, an ex junkie, and had junkie friends. Go ahead and write this off as an anecdote, but it's an anecdote repeated thousands upon thousands of times.
Illiterate or not, with this system, you can "read" the order at a glance rather than having to read a list of items or decoding a set of symbols. That might shave a second per order.
Another point, ink in markers run out and thermal printers frequently run out of paper at inopportune times. I presume condiments are well stocked. No hunting for a new marker or fetching a new roll of receipt paper with this system.