1) What Machine do you own? Include the maker and model number please!
2) when did you purchase it/how old is it?
It's about 70 years old. I also know of someone who works on a treadle.
3) How much sewing experience do you have? (how long sewing, how advanced your projects are)
I mostly make historical type costumes. Renaissance fair, Victorian, etc.
4) what do you like most about the machine?
It's made of metal, not plastic. It might not poop out fancy embroidery, but it will keep doing what it does 70 years after I die.
5) what do you not like?
6) Would you recommend your machine to a fellow cosplayer?
Yes. It's not really ideal if you primarily work with stretch fabrics. You can buy a zig-zig, hem-stitch, buttonholer (and it makes FANTASTIC button-holes) attachments, but it's not designed to be the machine's primary function.
If you need a zig-zag machine or one that does "fun" stitches, I would go for the 401/501. I know a lady that has one, and have seen it in use.
I simply can't imagine owning anything else. Except I would have interest in a treadle because of the electricity issue and I would be curious to see if it was any quieter. I don't think I would ever buy a plastic machine unless I was into doing high-production embroidered patches or something, but that's just me.