I have recently used both the Mitel 5320 IP Phone and the Mitel 5212 IP Phone - both very similar. Mitel seem to have become the standard office phone for companies in the UK with a large proportion of offices using Mitel products.
The Mitel 5212 IP Phone does offer more than your standard phone - however it also leaves a bit to be desired.
The LCD display is big plus of the phone. It takes a while to become familiar with as there are so many options and not all the options are necessarily in the places you would expect them to be.
Regarding the aesthetics this phone does pretty well, looking sleek and stylish. The only complaint I would have is that the design team seem to have focused so much on the aesthetics that they compromised on the practicalities. Namely that the network cable can be difficult to fit as the space to fit it through is incredibly small.
That said the result is a good looking phone with all the cables neatly tucked away (once you do manage to get it in).
I use this phone at my work and do like the LCD screen that lets you see who is calling and whether it is an internal or external caller ID.
From a build perspective, the only niggle is that it's really difficult to fit the network cable in to the phone. The space through which you need to fit the cable just isn't big enough to fit your hand (unless you're a 5 year old child - and we don't have any of them working in our office). The cable (once fitted) is also quite easily dislodged just by simply moving the phone on the desk - so, it's back to hiring a 5 year old again to re-fit the cable.
Overall it is a good handset. The phone is relatively intuitive, which is lucky as the user manual that comes with it is not - there's a great deal of information in the manual that tells you nothing you need to know as a user.