This game is actually quite easy if you follow the following steps:
1) At the beginning of the game, EVERY round upgrade the gun. If you have to miss a round be very careful to notice the difference in fuzzles so you don't hit a 1 shot fuzzle with 2 shots. (will mess up you're bonus)
2) Repair Bots. These are quite helpful, as they repair your droid while you're battling. However, Don't upgrade this until your gun is at max (if you can't make it this far, you should die. lol, j/k). If at any round you can't afford a gun upgrade get one upgrade in the repair droids.
3) Side Radar. This is useful in detecting the fuzzles on the side. But if you're quick enough, not necessary until you've maxed out the gun and the droids. (Also, I noticed that currently, if you buy this in the 1st game of the day, it'll stay with you the rest of the day. I don't know if this is a glitch, I'll let you know if it changes)
4) Those are the 3 things you need, the rest is counter-productive.
a) The Smart Bomb does clear the screen, but negates any bonus you've accumulated.
b) The Stun Bomb slow them down, but decreases the amount of Fuzzles you come across, decreasing your score and credits.
c) Hull Repair, If you've followed my instructions, you'll never need this. The repair droids (when upgraded to the max, 8, will repair itself.
4)Shields, are fine. They protect you from the Fuzzles you miss only. Mines will bypass the Shields.
5)Mines. They come in only 3 different paths. You should only blast the ones coming directly at you. If you miss, it'll count against your bonus, which you don't wanna do. And they don't count towards you're bonus.
6) And lastly the Bonus. If you can, always wait 'til the 10-hit bonus. I already tried to get more. It doesn't go past 3X's.

If you follow these rules, you'll do fine.