If you really want a
small S4, then yes, you should buy the S4 Mini. It's a very good phone
that performs well and has a decent screen. If you want Android phone
that's more pocket-friendly than most out there, it's a small step up
from the Sony Xperia SP.
If size doesn't matter to you, however, think twice. While it's a very good phone, it's not the best mid-range Android smartphone available. The 4.7-inch Nexus 4 still holds that crown as its cheaper £239 price tag gives you a quad-core processor, a similarly impressive screen and a nicer design.The 4.8-inch Samsung Galaxy S3 is now available for under £300, too, which also has a quad-core and a high capacity battery compared to the S4 Mini. If size is no object, we'd pick both before the S4 Mini.
If you are weighing up whether to get the S4 Mini or the HTC One Mini the latter feels like a more impressive 'mini' smartphone, but is still more expensive at £380 - we'll be posting our review of the HTC soon.