Could do yeah like
@Pulseammo . Or you could buy your kit outright your and add any PAYG SIM. Doing it yourself allows you the benefit of trying other carries. Whereas 3 kit = 3 network only. A certain well known place online usually gives 30 day returns. Or elsewhere will do 14 days return by law.
Obviously just check the returns policy from whereever you end up buying. But yeah, test it and if not happy, send it back and get your refund and cancel the auto-renewal on the PAYG SIM.
A v.quick look online. TP-Link Deco X50-5G = £249.99. Huawei 5G CPE Pro 2 = £279.00. ZTE 5G CPE MC888 = £178.80. ZTE MC888 Ultra = £329.00. Zyxel FWA510 = £370. Just as an example of stuff you can look into. Only thing to really check is that if you do buy 3rd party, check it supports the bands used by providers in the UK. (Most do but always worth confirming).