I like to play with the "no bullet clearing" handicap on, but the texts that appear in the middle of the screen are distracting to me. It would be nice to have an option to remove them.
The game hangs for a while if you put a very large number in the 'custom' box. This can be resolved either by putting a cap on it or by using some maths about series to calculate the costs more efficiently.
Oh, THANKS TO RA! Someone noticed it! XD Good, you achieved the "Eagle eye" badge!