I did this. 8 hours of torture and I have the medal for hard achievements.
For starters, everything that Fioresa says is WRONG. You get penalty for EVERY hit, no forgiveness, no fuck-ups whatsoever allowed.
Let me tell you something. The game starts pretty cool. It's hard, but you can get better and improve yourself. Basically, the first 7 levels are doable in 30 minutes.
Then comes level 8. It will take you over an hour to beat that level (but only because of the last wave with vice-boss).
Then, it will take you 2 more hours to beat level 9. The constant spam of the white shits is more than annoying. But eventually, you upgrade yourself enough to beat it (hopefully - for you). Then, if you hate yourself enough, you can, like me, try to beat these levels without getting hit. And that will take you minimum 5 hours, if not more (depends on your determination and stubborness, mine is pretty high). As a matter of fact, the only thing that will actually stop you from getting the last medal, will be the constant spam of the small ships, who are very fast and kamikaze-like.
So remember, if you feel like punching a wall during that game, you were warned! It's not for easily frustrated (unless like me, you are fueled by anger).
Frankly, I wish I would give you some useful hint for getting the achievements.
For level 8, it's important to have high damage, high automatic damage, and mulitply critical. For level 9, it's mostly damage, multiply critical, and speed powerup. All really highly upgraded. Plus some luck - if you are surrounded from both sides by white shitps, you can very well restart. Every other upgrade will also bring you closer to the goal, albeit it will be very small steps.
As you can see, the author of the game made a very cliche mistake - he artifically extended the gameplay, by making the last 2 levels doable after grinding, and barely achievable, no matter the grinding. For that alone I was thinking of giving it zero to be honest, and frankly, I don't really know why I didn't. I must be getting really soft. Or maybe I see a potential, despite the game being quite generic.
What could be done to improve the game:
-cheaper higher upgrades
-automatic turn-on of powerups (at least for fast shooting)
-much less grinding
-less little ships in level 8 (last 5 waves)
-slightly less white ships in level 9
-more efficient auto-damage (it didn't do shit in the final waves of level 8. and did no damage whatsoever in level 9)
or maybe, a more forgiving rating required for 3 stars that allows a fuck-up?
I might sound harsh, but once you play this game, you will say that I was being extremely polite.
Goddamn I am tired.