"MCU break" services start at just under 1k$ and go up to a few k$ USD, the last time I checked. They're mostly based in the Far East (I'm not surprised at the author of this page) and while a lot of people may think "IP theft", they're very useful for right-to-repair, although at the higher end of the price range; if you have some old very expensive machinery to which the original company has long discontinued support or even no longer exists, the price doesn't seem so high anymore.
You shouldn't completely rely on the code you put out into the world in devices remaining secret. A sufficiently capable adversary will likely eventually get your data.<p>Whether you're talking about a $0.30 MCU with the lock e-fuse programmed, or a several-hundred-dollar (or more) SoC with triple-redundant power-management/security cores booting using unit-unique payload decryption keys burned into security fuses, the adversary might be able to get what you're trying to protect.<p>How paranoid you want to be about readout protection will vary depending on your goals. If you want to do a decent job blocking reverse engineering of a product to impeded clones being produced, the lock bit might do the trick.