Those reactors are science proof of concepts, whereas these new ones being built and ready for around 2025 are demonstrable ones that are actively used to showcase to investors, public and education alike. The new Oxford one is the first of its kind by that nature alone and whilst it is not the size of an actual Fusion reactor (it is 75% scale), it is designed to show how viable the technology will be in real world use.
It's another experimental test reactor. A "science proof of concept", as you put it. The difference is that it's funded by a business rather than by a government. It's also
at least 11 years behind schedule and that's assuming that it works as planned in 2025. Which might or might not happen - it's an unproven method of creating fusion.
It's funny people always say that scientists keep saying it's "30 years away" - The actual increase in output has been improving every few years to the point of now where it's actually usable for actual studies and use once complete.
Fusion has been usable and used for studies for the last 60 years. None of the existing test facilities are useable for anything else at the moment since they're nowhere near q=1 let alone the much higher figure that would be necessary for useful power generation. The record is q=0.67 and none of the existing facilities can sustain their maximum output (that record-setting run lasted for 0.85 seconds).
It's true that there have been significant improvements over the last 63 years since the first working fusion reactor. And commercial fusion power stations are still thought to be 30 years away. The issue is therefore that commercial fusion power stations were a lot further away than people thought it would be in the 1950s. Which is no surprise - look at the other highly optimistic predictions that didn't come true.
Commercial fusion will happen in our lifetimes, this is pretty much a given. The UK gov has set a date of 2050 for the country to be net zero which gives a 25 year buffer to work with if the General Fusion reactor does go live from 2025.
The fact that a UK government has said that by 2050 the UK will produce no more carbon dioxide than it absorbs does not make it a given that commercial nuclear fusion will be made to work any time soon. It might well be, but that won't be because a UK government has set an arbitrary deadline for something else and set the deadline for long after that government will have ceased to exist.
And that General Fusion reactor is a test facility that's already at least 7 years behind the time the company first claimed to be able to have it working by. Not just working but attaining a sustained q>1. But it doesn't yet exist at all and it's unknown if it will function as well as the company hopes it will. It's a test facility. Not a commercial fusion power station.
I've seen a lot of optimistic claims for a lot of things over the years, especially when there's money and/or publicity to be had. Some of them worked out, usually rather later than initially claimed. Some didn't. A few were scams. The way the system works, especially for privately funded research, strongly favours convincingly made bold claims over more realistic claims. See Theranos for the most famous example of the worst end of the results of that system.
I do think that commercial nuclear fusion will probably exist within the lifetime of some people alive today. Probably not mine, but probably some people alive today. Probably. A lot has been put into it and we're about on the edge of a situation where investors can consider it potentially profitable to fund research into fusion. Which, of course, will ensure that if it does work then the cost to consumers will be much higher than it needs to be.