"They don't work, because the US government's modus operandi is compromising machines or forcing users to provide access to their encrypted data."
I'm not so sure - at least as recently as 2013, Lavabit showed that even top level US govt targets had some realistic reliance on properly encrypted 3rd party email providers...
The "dragnet" is the thing that's potentially useful - if it's difficult enough for them, they can't do warrantless "full take" surveillance - even for non US citizens, then choose to individually target you later based on a complete historical record being open to keyword/"selector" based searches.
(And for the appropriately paranoid - even Levison's comments back then suggested the thing he was prepared to fight and maybe go to jail for was handing over the SSL key that'd have exposes _all_ users. Reading it the right way suggests he may have sold Snowden out on his own - and I can't exactly say I wouldn't have done so myself in his position - but he was principled enough to not hand over the keys to the entire userbases's security. I sincerely hope _I_ never have the protection of privacy of a user like Snowden being my responsibility while the full pressure of the US government bears down on me. I strongly suspect my strongly-held personal principles would not stand up to that...)