As someone who recently went on the contract at £22/month I can say for sure its absolutely no good for gaming as there is way too much contention.
In my area Three can be anything from 2Mbit to 16Mbit upload with random ping spikes as high as 2000ms and a ton of packet loss. Downloads can be anything from single digits up to 50Mbit. I REALLY wouldn't want to be relying on this as my main connection.
Kinda annoying I missed out on the newer router but then I'm using the SIM in my S10 alongside my O2 PAYG SIM for calls, so I'd probably never use it anyway.