Yeah that was fun, very much enjoyed the puzzles.
Couple of things. Since I needed to end the "tutorial" level by throwing the magnet to open the gate, I was a bit surprised when the first real level just finished when I got the key. I had been primed to believe you finish a level by throwing the magnet into a tube to open a gate, so that was a bit jarring.
And secondly, I know it's only a demo so I don't know why I expected it, but I assumed unlocking the final gate was going to lead to a mega super hard puzzle, so it was a bit disappointing when it just said "Thanks for playing".
Ok suggested improvements out the way. I did really enjoy it. The puzzles were a nice level of difficulty, the magnet was definitely a core game play mechanic, and it left me wanting lots, LOTS more puzzles. Feels like something you could play for hours, or jump into from time to time to complete a few puzzles.
Keep it up, it's awesome!