It was difficult but fun! It is interesting that the player has to maintain a certain speed because if you play slowly and carefully, the yellow bullets will fill the screen and you will get stuck, and you won't gain any distance at all. I managed to clear it once and it was a great accomplishment!
Wow, you are playing way-way different than I was. I did fast up-down motions with the mouse, granting huge distances within short time. It filled the entire screen with crosses of all colours, which forced me to draw a slow pattern waiting while all of the spawned crosses to clear, allowing me to proceed with the pattern. It is much more risky, but as each run is vastly shorter I think it pays up in the end