DL4 sucks tone but is an amazing pedal.
I would have to say that with the expression control it's a totally different beast.
If you're getting it modded it's worth the expression mod unless you prefer a rocker pedal for control. DL4 Mods
For this, I'd have to say that a Line6 M9 would probably be worth the extra cash if you're getting a DL4 to mod, but if you have one already, mods are a great way to go.
I have a Pigtronix Disnortion that, to mod properly, costs about the same as a new pedal. Something to consider weighing effectively.