My current favourite device would have to be this skin analyser.
I picked this up from amazon and it was delivered at the weekend.
I thought I knew my skin quite well before this device arrived and I have to say that I was correct, however, this has also taught me so much about my skin.
I may start doing reviews of products now that I can add an actual reading on my skins reaction to it rather than just talking about how it makes my skin feel.
The device has a memory function for 5 readings which is really helpful so that I can remember my skins reading before a product/from the previous routine.
Obviously, because the price point was so low it may not be perfect but I don’t think its far wrong because of the feeling in the skin correlates with the reading on the device.
I would definitely recommend picking one of these up if you are interested in them.