One advantage it has though, is the attacker won't necessarily know the flash drive is holding coins (you could just be using it as an OS installer after all, like majority of the populace) unlike hardware wallets, so they could be less prone to thievery.
This is true, but I still wouldn't rely on the thief not discovering the coins for their safety. If you are storing coins on a plain USB drive, you should be encrypting it.
I'm not sure what kind of equipment is needed and whether Ledger has some protection to prevent such hacking attempts (in case your wallet is stolen).
There has been no demonstrated successful physical attack against Ledger products, but that is not to say one doesn't exist. With an electron microscope and enough time and expertise, then it is like that even the secure element will be crackable and the seed able to be extracted, but we are now probably talking about in the order of weeks at a cost of several hundred thousand dollars. This differs obviously from Trezor wallets which can have the seed extracted for less than a hundred dollars in the space of a few minutes. Any hardware wallet shouldn't be viewed as infallible, but rather as a mechanism to buy you (hopefully plenty of) time to move your coins to new addresses.