I've been using a
mifi router and Virgin SIM card at several adresss in the UK. I've had this for just under 12 months. The router was £35, a one off payment. I pay £32 per month for unlimited data allowance and maximum 10 Mbps download speed. It's on a rolling month by month contract. It has been fine in the UK. I watch tv, stream nexfix and other streams (football from other sources than Sky

). If the router was 5g the speed would be quicker but the connectivity worse that's part of the deal but I just use 4g.
When I bought the
mifi I was told I'd be able to unlock it from virgin after 1 month. I wanted to do this so I could use my EE SIM card ( from my mobile, to use that allowance) with it, or any other, should I wish. It took an age to do ( 4 attempts ) and as part or that process I complained and got the £35 I originally payed for it refunded.
I'm in France at the moment and part of their "fair useage policy" I'm limited to 25gb per month. I checked and every mobile operator in the UK has a this kind of restriction in one shape or another unless it's a very low allowance to start with. Or if you are with EE, as part of their response to Covid you will be "seen" as being in the UK and not in Europe.
Again I've used it at a couple of different locations and it's been ok, not as good as UK but to be honest but I'm in more rural areas.
Overall I'm satisfied with the set up and will continue to use it when I return my home address next week. Virgin customer service is not the greatest imo but now I'm set up and running I'd recommend the network. If you are at a static address you can check mobile network coverage in the UK on their website.
Regarding data allowance someone earlier said use a VPN so you wouldn't be seen as being outside the UK, this wouldn't work regarding data allowance as, I think, and stand to be corrected, the network you use can still be detected somehow? I use Surfshark and can't use BBC iplayer here or Sky exactly as you can in the UK. If anyone uses a different VPN with better results please let me know.