A must have accessory http://www.torchdirect.co.uk/led-lenser-holsters/led-lenser-intelligent-pouch.html
I have the Eagletac ones which are also recommended.
The TN31 is a big light for a handlebar and light output will definitely be comedy and will run for ages but does require 3 high quality batteries to do so.
My choice would be 2x VG10s as you use less batteries and can thus keep more spare if needed. I reckon you'll easily get away with just 1 VG10 though, it does output a lot of quality light! Get decent batteries and you'll get well over an hour on max brightness although medium is very bright as well.
Realistically do you think you will get 3 hours out of it though? Also is it bright enough to light up super dark woods on spread?
The reason i was keen on that TN31 Mrk has is that the picture he posted really makes it looks amazing!
The size is the only down factor, but there has to be a way to mount it to the bars ...