I have three currently. Just gave my Sony 600 away and sold my 350 because a friend desperately wanted it.
I got the Kobo mini to replace the 350 for reading on the bus, or putting it in my pocket in case I want to read when I am out. I actually read on it the most
My Sony T1 was my balcony reader for night time, although I do read other places.
I bought an Aura and am not overly happy with it. The mini seems to work better overall, and the Sony is far more convenient and much faster collection-wise. I am away working for the summer, so no balcony reading
but I may like the light better on the balcony, if not I will sell it.
I do use them all regularly. The mini because it is so light to hold and I like the touch to turn pages even if it often turns two, or goes backwards instead of forwards. Sad to say I gotten of used to that.
I have different books on all three, so sometimes I switch because it is less bother than having too many books on the Kobo and slowing it down. If I don't hit on something right away on one reader, chances are it is in the T1 as it dioes not seem to be bothered no matter how many books it holds.
Still I will likely buy another reader in the fall. Maybe two if I sell the Aura
I like gadgets, I use them all, and overall have no problems spending what most of them cost for a new toy.
Helen