After a lot of research I'v ordered one of those Pirelli MT43's should have it next week.
As I understand it the Pros and Cons are:
Pro's
Unbelievable traction on dry dirt, rocks, roots, wet tar, wet rocks
Good traction in sand although some complain of a "push the front" effect when trying to turn
Apparently very good in "certain types" of mud, cant quite make out what they mean because others complain about the mud performance
Good on tar - max speed 93mph which basically the bike's top end. I very seldom go anywhere near there (150 is my max cruising speed on highways more normally around 140) so its not an issue.
Cons
Square profile makes it a bit unpredictable in high speed corners on dirt - apparently tends to let go suddenly - this worried me almost to the point of cancelling (my speeds have been creeping up steadily on gravel - tend to blast along more often than not) but enough people seem to really rave about them to make me want see how they go.
Not a great tyre if your riding style is to spin the tyre through all obstacles and corners, it doesn't like being spun. I find the Husky tends to spin the current Heidies (note its not MY fault but the bikes

) quite a lot, but I really like the trials style of riding ie good balance and grip and finesse rather that just balls to the wall through everything - I'm hoping we'll get along in this respect.
Useless in deep clay type mud, but then nothing but a proper knobbly is going to help and even they will have their limits.
Not good for rear braking - not sure why but pretty much everyone says this - I hardly use the rear brakes at all so that doesn't bother me.
Not good if you like to break the back loose or lean right over in corners - apparently they don't break loose until they just let go completely - a bit worrying - again enough people rave about them to warrant a try.
2000 miles is all you can expect. They aren't that pricey and prefer having good traction to having a tyre than never wears out.