Thanks everyone for the answers.
The NL cart that I have is the same kind as the yellow one posted here http://chipmusic.org/forums/topic/12226
artridges, except that it's gray but the PCB, at a quick glance, seems to be the same.
I can't remember which NL it is to be honest, it's been many years, I would have to look for the manual in a pile of boxes. It does not have the arpeggio and gives access to three voices only so it's definitively < 1.3, maybe 1.2 ...?
Looking forward to learn more about what this flasher device could allow with such a cart.