Your hat looks great.
I use circulars now for everything I can get away with, scarves and other flat stuff, tubes, whatever. If you use longer ones even when you do flat stuff it's a lot more comfortable, no more poking yourself or others with long needles!
The hard part of the kitty hat for me was picking up the stitches. I kind of ending up doing something that didn't look like SnB directions but came out looking right. Since it's picking up you can do it and tear it out until it looks right.
Wow, that's awesome advice, I have also gotten used to the circs