TL;DR - when buying spare Sindoh 3D printer filament cartridges, always get the type C cartridges so they are compatible with the full range of Sindoh printers. Type A or B cartridges work in the 3DWOX 1 but not in the 1X or 2X.
Some months ago I got a 3D printer for an important customer project, and I chose a Sindoh 3DWOX 1 primarily due to the review and recommendation from Shahriar of The Signal Path, a super high-end electrical engineering blog.
These printers can use standard filament, but I mostly use Sindoh-branded filament in their cartridge system because it's just so easy to work with. Sindoh refills come with a smart chip that describes the filament ("700g of red PLA", for instance) so it can keep track of how much is left - it warns you if you're going to run out during a print.
There's around a 30% premium for Sindoh-branded filament, but it's so convenient and reliable that I mostly stick with it.
And I loved this printer enough to get a second, this time a larger 3DWOX 2X, with two extruders plus a larger print volume. This is a great machine and it's been really helpful with the workload; sometimes I have to turn out hundreds of a thing.
But when changing cartridges I found that one of my spares from the original 3DWOX 1 didn't fit. Huh?
Turns out that Sindoh has multiple cartridge formats, and the 1X/2X use the Type C cartridges, and older Type A cartridges just won't work in these machines. I think the functional difference is the filament-drive rollers are a bit different and have a different gear, but the printer enforces this restriction with a post that indexes into an alignment hole on the cartridge:
That hole is merely there as a lockout for older cartridges, and serves no other functional purpose. This was an unhappy surprise, as I had a fair number of spare older cartridges.
So: when shopping for cartridges, always buy the ones marked explicitly as Type C even if you have a pre-1X/2X printer. Type C work fine in the older units, and you never know when you might want to upgrade.
When shopping on Amazon, Sindoh sells many combo packs of filament + cartridge, but my experience is they are always the older type, so if you want a Type C, you have to buy them separately (and specifically).
I've taken to marking all my cartridges with a small P-Touch label that shows the orientation and which printer it goes in so I can tell what's available on my shelf, and the orientation arrow has been surprisingly helpful.