I had a chance to try something the other day,

a AR15 with a Partisan forced-reset trigger.  True drop-in trigger mechanism, no gunsmithing required, and yeah it worked.  Nicely.

Definitely fits into the category of 'Fun at turning money into noise'.

Added: it's the kind of thing I'd like to own just because the gun bigots and hoplophobes are so pissed that commoners might have such things.