Action76 is correct for the placement of that plastic.
Demo Man looks amazing with LEDs. It's the first machine that I did that way, and it looks better than regular bulbs.
As for the swear roms, if you need to upgrade your regular game code, it's worth it. Mine had some sort of really early code on it that had like half the game missing, it was incredibly bad. Got the profanity roms and the gameplay doesn't suck. But, beyond that, they are sort of funny the first few times and then that's basically where it ends for me. If you find naughty words really funny, then they're by far the best out there, but otherwise it doesn't add enough to the game that I'd suggest doing it for the price they cost.
The flipper handles are neat I think. They help a lot in nudging, and people who would never nudge other games nudge a bunch on DM. I think they attract players too, as DM earns all right on route, and for a game with a crap theme and basically no "instant see" toys that is almost 20 years old and no one remembers, I think that gimmick is what makes people drop their quarters in it still today.
I have a love / hate relationship with the game. The scoring on it is totally screwed up so the only thing that makes sense with the claw if playing for points is Lock Freeze, Lock Freeze, Lock Freeze, Lock Freeze, etc... but, it's oddly the one game that I have no issue not playing for points, and instead playing for as many combos as possible, or just because it "feels" good, or whatever. Mine won't be going anywhere anytime soon, although I'll be the first to tell you that it is horribly flawed as a title. It's just darn fun to shoot.