I would be wary of the $300 machine, anything could be wrong with it. Everyone says, "Tension problems" when they have no idea what is wrong. SOMETHING is wrong with that machine....who knows what....might be minor...might be major. OK....I'm suspicious of everyone.
I am not a big fan of FW's. My first one i got for $20, worked on it, sold for $250. I have one now, paid $100, needs a little work, and I plan to sell for $250, or less. I miss the needle up/down feature on vintage machines. They do sew well though.