Yes and no.
Appwise you can't login.
Webwise you can - but very little control i.e. can just check it's "working"
If though you get within range of the gateway you can login to its local Wifi. But! ( here's the thing I didn't know ). Though there's a serial number and password on it ; apparently that password gets changed once the installer sets it up ( so you can't log into it because you are believing the password is as it says but it isn't ).
So once you get the correct password you can login as long as you are in range of the gateway. You can see it's working; but you are looking at local data not Tesla server data.
Since install the PW has had no real issues ( a few hiccups in the App ) ; unlike SolarEdge who dick with the cloud based stuff every week or so causing all kinds of strange behaviour.
What took the time today was contacting everyone and obviously me learning a bit more about the PW.... - next time I'll have a better and quicker way to check things.