I also noticed it gets a little slow if you have a lot of attacks going out at once. It only came up for me when I wanted to send as many as possable from one circle to another so I spammed attacks to get them out. A possable solution to that would be having a selector to set what percentage you want to send with each attack. that way you could put it up to max and clear out a circle with one large attack, instead of several incrementally smaller ones. Just an idea.
Loved the game. Simple concept but very entertaining. I would love to see more levels or a harder option though, because I found it a very easy overall.