This has a ton of potential! The idea of flipping between classic asteroids and reverse asteroids is really unique and definitely fun. The speed issue you mention in the description definitely makes it a bit too challenging but it was fun despite that. I'm not sure if you are doing the movement with a rigidbody or another way but if you are using a rigidbody, you could add more drag to it and that would help even though its space and you normally wouldn't have drag. When you have to manually slow it down completely it can make it feel like its hard to control.
I love what you did with the thrusters though. Such a small detail with the animation but its a nice dose of realism that I really liked. Overall fantastic idea and I think with a little bit of extra polish it could be a really great game.