Thank you, and don't worry, yours is a very valuable sample point! I'd love for everyone to enjoy my games, not just shmup veterans ^^ (honestly I don't think my games cater to them anyways lol)
Regarding invincibility - there is indeed a window but it's really short, 0.1s (so it takes ~1.6s of constant damage taking to die at 16 hp). I'll probably keep it that way, but for the relaxed mode will likely double the starting HP, and adjust patterns to be easier to predict and "solve". Again, thank you for playing and for the feedback!