I'm one of those people who change my phone a lot, and after a few years of having android phones getting bigger and bigger I decided to trade in my Xperia Z and go down a size to the mini....and I haven't been disappointed!
Although the mini doesn't quite have the lovely build quality of the flagship HTC One, it is still a wonderful thing to hold in the hand and feels like a quality product. It also has much of the functionality that most people will ever need. It zips along at a good speed, the HTC apps are generally very good, the display is excellent, sound quality is good, and I think the size is perfect, so much more pocketable than the around-5-inch phones.
--Its slimness is lovely, but not too practical as I do find it slippy in the hand. However the HTC-made hard case sold separately (with the changeable colour ends) is very stylish without adding bulk and also helps to keep a good grasp of it.
--Silly thing, but because the top and bottom look very similar I often find myself trying to press the usb hole to switch the power on (the power button is in exactly the same position on the other end of the phone) :)
--It has not got the power/memory/features of the One, but then I didn't expect it too...
-- ...nothing else I can think of!
I love this phone! Such a nice size and design. I can thoroughly recommend it.
That said, the One is getting cheaper and now there's not a huge amount of price difference between this and the One Mini, so do think carefully before purchasing as the One is certainly a impressive and powerful phone....but that bit bigger!