Hi Bowdon, both you and ISP review are a little out of date.
Three have had unlimited data since around Black Friday for £20 a month, which you can use in a modem if you want to.
The specific data sim that you linked to is more recent I believe.
For answers to your questions see this thread and the ones that are linked to in it.
https://forum.kitz.co.uk/index.php/topic,23028.0.htmlThe biggest issue with mobile broadband is CGNat and the lack of a public IP, but if you don't game and don't need to access your network remotely then it's probably fine.
My speeds at home on my phone reach 100/30Mbps via Three 4G, but very much depends on location and congestion.