These Billy add ons actually seem solid, unique and interesting.
Iridescent Brick: Undetectable after a 5 second sprint. Makes BBQ chainsaws terrifying. Every time someone hears the chainsaw they immediately have to go for cover even when they think they're safe. Combined with the Apex Muffler or Off-Brand Motor Oil for decreased sound range (or silent), and this will be an absolutely terrifying stealth Billy.
Tuned Carburetor: lower charge time, base movement speed. It's actually a good trade off, you want easier one hit downs, then you have to rely on your power more as your base speed is lower.
Big Buckle: Possible synergy with M&A to have a tiny terror radius after long sprints. Could work well with TInkerer to grant you Undetectable as you approach a gen, and retain stealth once you're there for surprise attacks.
Lopro Chains: While it removes the one-hit down, this turns any pallet into a risk. It's like going against Huntress, it forces survivors to drop pallets in less convenient ways or risk taking a hit as Billy charges through. Unlike Huntress, he also doesn't then have to kick the pallet after the hit to keep chasing. For all the complaining about Billy's chase being hurt, this seems like a major game-changer that could clear all the pallets off a map quickly and efficiently.
There are obviously some crap ones. Mother's Helpers seems downright useless, Black Grease is largely redundant because blinds don't generally last long enough after you break a pallet to be a concern. I get that they want to play up the "Billy = Lightborn" aspect, but they don't seem worth using ever. That said, all killers have some turd add ons, and at least he doesn't have a goddamn haemorrhage or blindness add on.