I have one.
I find it very good, like Jason has said i have drawer's full of scientic calculators and can't work them as they all have different methods of working.
Where this one score is that they have put some thought into what an engineer does.
Switching between inch and mm is just 3 presses, no having to enter 25.4 at any stage, just enter the figure, press mm or inch to define what you are starting in and then press the opposite button.
Works in imperial or metric threads, although the book is predominantly imperial they tell me they are working on a mertic / combined book.
The bit's I use most are tapers, enter lengths etc and it spits the taper out and measuring over thread wires which it does without any tables.
John S.