So most of my thoughts have been done above: but some finer points-
No matter how good or expensive a light is I'd always like to have 2 on the go: this comes from my experience with the earlier magicshines that would switch off or change mode in the rougher sections.
Basically I'd prefer 2 cheap lights to one dearer / more powerful one.
But if you insist on going for one light I'd go for 2 smaller batteries rather than 1 big one. They can & do fail (or slowly get a lot worse). Also you can have one charging while you use the other.
btw you should get "comfortably" - 5 hours from the normal mj872 battery with judicious use of the saver-low-med-high settings.
Last useful point - I had an xml based light and found it to be a "spotlight". To me it wasnt ideal for on a bike except for on the lid - but that may just be me. I sold it on.
then you pay 20% vat and handling,
I've never ever had to pay vat / handling from hong kong. I may be lucky - along with everyone else, but the PITA is in returns / warranty.
"will I die" - yes. But if a half decent light gets you out exercising over the winter then that eventuality may be deferred somewhat.