https://www.mycle.co.uk/products/commander-fat-tyre-electric-bike?variant=42993630150898
They have basically used the example of mid-drive motor ebikes being legal and applied it to a hub motor ebike. It has taken the Chinese manufacturers and UK importers a long time to realise how the European legislation works as it doesn't make sense but yes you can have such a fat bike and legally ride it on the road.
However it has to be certified as 250W which as we all know is a complete joke with a huge range of different power ebikes all calling themselves 250W on the European market. The important thing is it mustn't assist beyond 15.5mph. As for the throttle some only operate while pedalling which is completely legal, others are restricted to something like 6kph which is legal and others may not function at all at the 15.5mph speed setting or just be disconnected. These ebikes are still slightly less powerful in wattage terms than many mid-drive motor ebikes but there isn't much in it.
Probably the best thing about these fat bike ebikes is the wider hub motor allows for more windings so they can be more competitive in torque with mid-drive motors and even deliver similar torque for less wattage.
The Gogo model doesn't appear to be certified for the European market but I doubt in actual electronic terms it is much different to the Mycycle model in overall wattage. If you want to make it legal of sorts I guess you need to put a 250W rating sticker on it and not unrestrict it. There has been discussions about this on the pedelec forum. The motor will operate at 250W and that is all the certification tests for not what the highest wattage it will take is which is incredibly strange and manipulative certification.
So yes you can have a high power fat ebike for climbing hills just like you can have a high power mid-drive e-mountain bike but you cannot have it with a full 15.5mph twist and go throttle.
There is however a motorcycle style ebike with fat tyres that is now legal with a high power probably 750W hub motor (classed as 250W) and full speed twist and go throttle;
https://pedibal.com/products/pedibal-cruiza-fat-tyre-electric-cruiser-ebike
That high power 80Nm hub motor ebike has to be individually tested and there doesn't seem to be any kickback/problem with having a high power hub motor and just calling it 250W same as mid-drive motors.
So there is now a single option for a high power hub motor ebike with fat tyres and full twist and go throttle but I personally prefer the larger 26" fat tyres over 20" so no legal 26" actual 750W fat bike with full throttle yet but perhaps pedibal will import one.