Englishal
Yes the running costs are impressively low. Whether it is enough is a different matter.
Very very approximately you are saving £110 per hour in fuel burn and maybe £45 per hour compared with a typical light single and perhaps £80 with something more adavanced over a similiar distance. So as a personal means of transport flying maybe 100 hours a year that represents a saving of £11K down to £5K a year.
However it is diificult to imagine that the depreciation isnt going to run at least 30K a year on a 42 over say the next three years. Of course the other operating costs should be much less compared with an older aircraft but I would have thought it is no where near enough to make good the difference.
If you can get 300 or 400 hours use a year (as a group or school might or some really dedicated private users) and the economics change drastically.
In short a group of between 4 and 6 pilots each doing 100 hours a year in a 42 could save getting on for £70K in fuel compared with a "normal" twin and getting on for £50K compared with an advanced single. That covers the depreciation and the maintenance costs will be a lost less anyway. At that point it looks even more attractive.
Of course unfortunately there will soon be some duty on A1.