@Optimos is 100% right. After being assigned to the 10 saws mission during an hour of playing I haven't been able to get that shooting power up even once. It's like the game wants to tell the player "screw you".
1. Most of the times when you hit the rainbow balloon you get nothing;
2. Even if the 3 slots do match-you get everything but the power up you need;
3. And even if miraculously you would get that power up you got absolutely no guarantee that you would get any saws to destroy before the bonus time expires. It happened to me many times before I unlocked that mission.
So as it was already mentioned by one of the other reviewers this is an almost pure luck achievement. Creating it as such is a pure stupidity and I very rarely describe it like this.
I got no idea what was its purpose, to force the players to visit the game more times than they should? For more revenue? In fact all of the other achievements - if the game was not forcing the player to get them in sequence - could have been obtained during a single playthrough, so that may have been the point.
As for the achievements - their placement in the sequence and their points value is also a bit of absurd. The one for hitting 5 violet balloons should be one of the very first ones since it is extremely easy, while for example hitting 10 red ones requires more effort - and luck. No idea what the author was thinking when planning it like this. Also collecting 500 acorns and saving 6 piglets would be easy.
As it was also already mentioned, the upgrades give you basically nothing except the ones giving you more hearts. The game itself tends to be laggy, especially in the caves for some reason, so any speed upgrades are pointless. In fact, why would you want to move forward faster? What advantage does it give you? Completely none.
And last but not least - the author himself failed to obtain that 10 saws medal.