I have the Mega-Drive 1200 and have to say even with that one I am impressed with the light it gives out (though underpowered for anything getting technical its good on fire-roads etc and passable on any more). I would expect the 2400 to be sufficient and indeed am considering getting. The quality of build of the 1200 is good but as others have said the strap is not up to much (on rocky descents the light rotates round and points at the ground). I ended up unscrewing the strap from the bottom, attaching an exposure mount to the light and then using an Exposure handlebar mount (did not realise at the time that Lezyne sell separate mounts).
As above I am super impressed with the 1200 (which was initially bought as a back up light for a 6 pack). The only other issue is the cycling through various modes, which can be avoided by using on race mode (on the 1200 the lower setting is pretty dim, but on the 2400 its brighter).
I would happily get the 2400 in fact think I might – however my choice has also been confused by the Raveman 2400 which also looks good, seems a bit better for the road sections and also has a handlebar remote (but still requires cycling through the modes).