Recently, I keep hearing people talk about block builders, bundles, as if it's some kind of mysticism.

Honestly, how much do retail investors need to know?
I think you shouldn't push yourself to become a researcher: remember one thing—
the transactions you send out may not be included in the block in the order you see;
someone might "bundle" and jump the queue or insert themselves, so for large or sensitive operations,
don't be greedy for that tiny fee savings;
try to use the default protections of reliable wallets and avoid changing parameters unnecessarily.
If you want to understand a bit more, it's about knowing that "private bundling" can reduce the risk of being targeted,
but don't blindly trust any channel to be 100% safe.

These days, hardware wallets are out of stock, phishing links are everywhere,
security awareness has increased, but some people panic and start clicking "airdrop claim" links everywhere...
I'm actually more cautious—I'd rather miss out than sign things recklessly.

There's also a little mindset:
a while ago, I saw some people hyping up bundles as a universal talisman,
so I quietly unfollowed them;
later, I saw someone explaining the boundaries and costs in plain language,
and I followed back.
Anyway, I trust on-chain execution more than those few overpromising words.