I'm no attorney, so I can't speak to the legally binding nature or how it would hold up in court.
Most countries have laws that make digital signatures legally binding. However, there is really no way to do the e-signature yourself and be able to prove it wasn't changed after the fact. You can save it in your database, or even make it a requirement in your web form that can't be avoided, but someone still might argue that it was falsified later and that couldn't really be proven.
The same can be said for a signature really. Unless you have a notary there to stamp a seal and verify the signature, it could be back dated or falsified as well. So, I'd say the level of security you want depends on the value of the items you are verifying. Nobody is going to take you to court for a few hundred dollars to try to claim they didn't provide an e-signature (particularly when they are lying). However, if you are signing deals worth thousands of dollars, I'm sure you could find a lawyer to take that case.
E-signature by a third party is equivalent to having a notary witness the signature. If the nature of your business calls for that level of security, then I'd say integrate it. If you just want something to point to and stand by outside of court then an e-signature is probably enough. You could take the extra step of saving e-Signatures in a separate table with no direct editing capability and save the timestamp and IP address of the signers and even encrypt a key that combines all of those elements into a unique identifier. However that could still technically be faked because it is on your server.
