The best I managed was level 3 and one bullet upgrade.
The music is incredible!
It took me quite a few failed attempts to realize that I was destroying myself by allowing the gun to come into contact with the ship. My focus was always on the enemies, reacting to their positions and attacks, so it felt 'random' when I would suddenly lose, until I actively tested the interaction.
The ability to hold down the fire button, or just have auto-fire as an option, would be a nice quality of life upgrade.
It feels like having a gun which moves independently of the main ship should be a huge advantage, but I never really got the feeling that I could do anything clever with it. Perhaps if I'd ever been able to save up for a longer string upgrade.
The one-hit death is also rough, again something that might be alleviated if I could afford a shield upgrade.
The circles the enemies drop and the bullets the enemies shoot are quite similar in appearance, which could potentially lead to problems. More so, though, it felt very difficult to destroy enemies effectively and move in range of the pickups. Which would be when the gun and ship tether would be a great advantage, if only the length was long enough for it to work.
So the feeling I'm left with is that the game would improve if I could afford upgrades, but I need what the upgrades give me in order to effectively collect the currencies required to purchase the upgrades in the first place. If that makes sense.