rdx.overdevs.com doesn't redirect to two different websites, it's a subdomain (which essentially functions just like any other domain).
The name being long isn't really a problem when most people just bookmark the sites they want to visit often and/or add the site to their home screen on mobile devices.
Moreover, using an alternate domain would incur additional unnecessary yearly cost & time to renew. The less maintenance these types of projects need, the better it is usually for them to survive long term.
Their generous offering of 10gigabytes of free storage along with a private, ad-free, end-to-end encrypted experience always sounded too good to be true. There was no way they could sustain that business model long term. At least they're giving users enough time to jump ship and have not sold their data to Notion (judging by their twitter replies).