And does this generate true randomness? Or is it just a placebo effect? I'm not an expert, but according to what I've read this is a not a good practice.
Care must be taken to securely generate keys since an attacker can steal stored bitcoins if it is exposed, transmitted, or generated with insufficient entropy.
Some websites feature a free open-source client-side paper keypair generators written in JavaScript. Using these is generally considered a bad idea and inherently insecure.
A web-based generator should not be used.
A generator should use an appropriate source of random numbers (entropy). This means that the generated keys aren't predictable. If the addresses come from a predictable or partially-predictable patterns like pseudorandom numbers [1], someone else who can predict the pattern can steal the balance. Ideally, randomness should NOT be human generated.
https://en.bitcoin.it/wiki/Paper_ECDSA_private_keysAlso:
https://bitcointalk.org/index.php?topic=101733.0https://bitcointalk.org/index.php?topic=153990.0You don't want to generate as a 'client'side', you can create in offline computer and yes, it gives true randomness.