I’ve been involved with making and analyzing some of those filters. For the most part they are a joke. Yes, they will catch a lot of the naughty pictures. But they are often (usually?) made by bored, underpaid workers at companies who mostly trade the same stuff back and forth or by organizations with other axes to grind. Depending on the axe La Leche League, the Anti-Defamation League and the Skeptical Inquirer might be banned while Bassett Hound Lust – which I fervently hope does not exist – could make it through.
And yes, LLL, the ADL and SI were filtered on one list I had a chance to examine some years back. Neo-Nazi websites and ones chock-full of malware made it through just fine.