https://community.enhance.com/d/642-easy-email-migration-ui/10
Its trivial to setup a docker container with the same interface you get with the free online impasync tool.
If you are a professional business you should never be trusting a third party with your customer's login info and emails to avoid 30 minutes (absolute max if you are not familiar with docker) of setup time...
Its logical for a customer of ovh, for example, to use ovh's tool. Whats not okay is a customer of xyz accepting migration and employee of xyz uses ovh's tool. The customer gave xyz access NOT ovh.