- Sounds sketchy, but if the same seller is on Cults3D as well, might not be a scam.
- Really depends on the printer / slicer. STL is the most universal, OBJ is also very supported. 3MF is usually tuned to a specific printer family, but you can easily extract a STL from that.
- That really depends how similar in size your arm is to the author. Scaling it up or down is usually easy, unless there are some tiny parts and you're scaling down. Also if you have massive hands, the printer might not be large enough. Or the printer in general might not be large enough for that model, that depends on the printer you'll be using.
- The material itself will be pretty cheap, though any service will obviously add a markup.
- I'd personally prefer Cults3D.
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