“superior” depends on the application. IMHO CF should never be used for something that will be handled regularly with bare hands. Also, IIRC the GF stays unsoftened to higher temperatures than CF, which helps when being used for e.g. a barrel mount. I remember a video of someone doing a mag dump on a presumably PLA frame where the barrel was flopping around like a freshly caught fish’s tail after a few dozen rounds.

If the license is NC, they can’t legally monetize it by demanding fees, that’s the whole point of the NC license. (I don’t remember where I found your file so I don’t know what license you put it under, but the other guy wrote that it was a NC license, so I’ll take his word for it.)

I would recommend registering your files with Copyright Office / Library of Congress immediately. I think I remember that your publication date was early August so you are still within the initial 90 day period. Copyright.gov has the forms and FAQs. The forms are self-explanatory.

It’s up to $15,000 of free money to you if you use the CCB, or $150,000 for statutory damages if you go with the regular federal court system – but you have to register the files timely for that.

DefCad has a long history of ripping off people’s designs in this manner. I remember people complaining about it regularly in /r/fosscad (RIP in pepperoni). Frankly I think it’s long beyond past due for someone to take them to task.

If they are using your files, you have a copyright on them which automatically comes into existence when you created the files and published them. They are in the U.S., so you can sue them in the U.S.

Under U.S. law, it is important to register your copyright with the Copyright Office (Library of Congress). If you do this in a timely manner, which means less than three months after publication, you can sue in federal court for statutory damages of up to $150,000 per file for willfully redistributing the files. Suing in regular federal court is difficult and expensive and takes a long time and you would likely need an attorney to navigate the process. There is an alternative, however:

You can also sue via the Copyright Claims Board at ccb.gov which has a simplified speedy process and which can get you up to $15,000 per file (with a limit of $30,000 per suit). Note, I do not know whether you need to have timely registered your copyright with the CO/LOC to do this. (You DO need to register it, though, even if untimely. I don’t know how an untimely registration affects the damages you can get with the CCB.)

Registration with the CO/LOC is simple but does require paying a fee. Last time I went through that it was $40 per registration.

You can talk to or even hire an attorney to help you navigate the CCB if you really want to, but AFAIK it is straightforward enough that most people can navigate the process on their own.

Edit: I noticed below you mentioned you published under a CC license. You still retain copyright, CC licenses just tell people how they are allowed to use the files, and is explicitly not public-domain. However, that may or may not complicate things with the CCB and/or regular federal court. You might want to talk to an attorney familiar with copyright law and Creative Commons licenses to figure out how much you can sue for.

Another edit: note, I haven’t tried registering STLs, STEPs, or other CAD type files ever. I assume they can be protected the same as software programs, but I don’t know this for certain. My work was mostly with commercial packaging (to be able to block counterfeiters).

Disclaimer: these off-the-cuff remarks are not legal advice. For legal advice upon which you can rely, please contact an attorney licensed in your jurisdiction. These remarks were made using 100% recycled electrons.