I have the Sony 350, which is also a 5" screen like the Kobo mini. I've had mine for almost 2 years now and love it so much that I bought a 2nd one as a spare for when this one dies.
I love the smaller 5" screen, the smaller size makes it so portable it fits in just about any pocket I have, which means I never leave the house without it. I originally bought it when it was on sale thinking I'd end up returning it for a 6" screen, but after using it, I fell in love with it. I have no problems at all reading on the smaller screen and have never missed having a 6" screen. I use it strictly for reading, nothing else.
I'd say for that price, you couldn't go wrong for a first reader. Some people say you have to turn pages more often, but it's just a slight thumb movement to turn the page, you aren't even aware of doing it.