There's a little benefit to etorque, mainly smoothness or if doing a lot of in stop and go driving you may save gas using stop/start.
It isn't the initial cost, it would be the cost if keeping the truck long term, after 8 years or 80k mile the generator and battery are no longer covered by warranty. Hopefully that clears up what I was referring to. For some people the 80,000 mile comes up quick.
I really don't know if it is any storage space that you would normally use or not, I haven't seen one but I have read it sits behind the back seat, not under it. I do stuff some stuff up behind the seat on my non-etorque but don't know if everyone does.
If you can go see one it person, it would be best.