First off, lag is a myth or a trait of a crap set up, right setup it wont make any difference, or at least none that you can tell by feel (disclaimer, yes there is a slight addition if you calculate it on paper, but your talking fractions of a second). Most people who perpetuate that refer back to a calculation that Andy F did donkeys years ago that was majorly flawed, assumed zero pressure in it and that gear changes happened at 3500rpm.
My car pre front mount,
My car post front mount,
on top mount 3500rpm = 250bhp, 380ftlb, on front mount 3500rpm = 280bhp, 420ftlb, same turbo, both on syvecs with same supporting mods bar the addition of a front mount (not a small one either hahaha).
Ebay coolers are hit and miss, get the right one (internal of the core is the important thing) and its fine, get the wrong one and it will be crap, airflow will be disrupted and it wont ever perform.
Other than the sound running without DV makes no difference to performance, it will however reduce the life of your turbo, some are more affected by it than others. I run a GFB DV and get chatter anyway.