We've acquired ImprovMX in 2017 and greatly improved the service (from a single DO droplet to multiple powerful servers to handle thousands of emails per hours).
Actually the forwarding doesn't seem to work so I may switch over to you guys :-).
I agree that the open-source part is the USP for ForwardEmail that we haven't. The thing on our end is that we have already thought about opensourcing a few parts of our service, but if we don't do all, it doesn't matter to do partially.
So instead, we plan to have an audit from an external service to guarantee that what we say and offer is aligned with the respect of our users and privacy. That's the next step :)
E.g. saying "if we shut down we'll notify you one week prior".