That’s not the cheapest three-pack mesh Wi-Fi (which is the Tenda MW3) but it’s a good step up from that kit if you’re willing to spend £89.99 rather than £59.99.
The Deco S4 claims to cover up to 4,00 square feet, 500 more than the MW3, and it also benefits from Alexa integration (for the guest network password) and a better app. There are two Gigabit Ethernet ports on each device, too.
One point to bear in mind is that the two satellites communicate with the primary directly, so this system is best installed where the other two units can be placed where they still have a strong connection, rather than in a line with the third one furthest away. Also, unlike TP-Link's more expensive systems, such as the P9, this doesn't use powerline networking tech to communicate using your home's mains wiring.
Nevertheless, with speeds of up to around 170Mbps, which is way faster than most UK broadband connections, then this budget mesh system is a bargain and will deliver considerably better Wi-Fi coverage and speeds around your home than an ISP-supplied single router.