Re: Oh bugger.
"Unlimited" tariffs are a bit pointless for comparison - very few people actually need to use more than a few GB of mobile data a month what with all the WiFi floating about for free. Even my kids manage to keep well under 5GB a month, in fact most months they are under 2GB*.
Of course, if you are in the habit of attending work Teams meetings at the top of a hill, you'll need all the data you can get, but a bit of TV or radio or social media on the bus or train on the way to work? WiFi.
So the real question isn't "what does unlimited mean, and is it worth £<n> a month more than 30GB?", it's "which tariff is closest to my actual usage?"
To take my kids as an unrepresentative sample, why would I pay £20 a month for unlimited data (Smarty) when they have never (so far) used more than 5GB. I might as well pay £6 a month for 5GB (or £5.40 each for two with 10% off) and use the £14 saved for something else. In a year or so that saving could have paid for a reasonable refurbished phone from somewhere like Backmarket.
I can even leave some non-expiring credit in the account just in case they need to exceed the cap.
M.
*I know this because my entire family is on limited data tariffs of various descriptions (all under 5GB), and I can think of just four occasions in the last (say) three years where the limits have been exceeded, one of those quite recently when an important work meeting had to be attended at short notice, parked in a WiFi-devoid car park with work kit which has no data allowance at all. 3GB wasn't quite enough for the full 90 minutes of the meeting.