We believe using an independent third party (like SignatureAPI, Docusign, etc) for electronic signatures adds value. If you host your own electronic signature platform instance, you act as both the authority and the signer/signee. In case of a dispute, this could make the signature difficult to defend.

That said, there may be cases where a self-hosted solution makes sense (eg in high-trust situations), and I always like seeing new electronic signature platforms come in and challenge the incumbents.