Thanks for the feedback everyone... I decided to take your advice and NOT buy the zision cutter, however much I wanted the cute nonstick scissors! I can get them for myself later... and I decided that i wouldn't get another Fiskars cutter - I've already got the big one and it's okay but not suitable for carrying around.
So... I looked around a little more and decided that I was happy with what I already had, and I bought another Carls personal rotary trimmer from Staples. I've been very happy with it (yes it cuts straight) and the blade stays sharp for a LONG time. The only thing about it is that you need to replace the rubber cutting strip at least once a year or it goes to shreds - but I've been using the shredded one for that long and it still works fine, it just doesn't LOOK pretty. I bought a spare cutting strip with it, but they were out of the blades... I just hope they're out of stock and not out of production!