I’ve got nothing contrary to say to that. Some of it I wasn’t aware of, actually.
Regarding its (the eponymous product, as opposed to their VPN offerings) use of mobile device VPN, the configuration profile & the tunnel it establishes is routed to an endpoint on-device as you stated. As I’m sure you are aware, the entire point of VPN is strictly to encapsulate traffic at the network layer (OSI model). Once packets exit the endpoint, there’s no indication that they came from a different network which is by design. Ergo source IP remains the same (as it is a local VPN), and traffic it filters is not distinguishable from regular device traffic so it should not make a difference with signups.
In my case however, the above is irrelevant. Signup was done from a Windows 10 Pro desktop with Adguard running locally which does not utilize a VPN to achieve filtering.
I’d be willing to test account creation on a freshly imaged laptop on the same ISP, same email domain with one of my other cell lines on the same account. Alternatively I can simply disable Adguard and wipe local storage/cookies and try again from the same machine, though I suspect there’s enough fingerprinting in use here that it wouldn’t work because of the prior flagging. Whichever you feel would be a more useful test.