Been very happy with my APC Back-UPS CS-650, which is available for ~£100.
It has a couple of battery-backed AC outputs and one non-protected output. All are female IEC ‘kettle’ sockets (type F, as you mention).
It’s sat in the cupboard under the stairs where it gets some good ventilation from a nearby air-brick. I’ve got a 10-way 13A socket extension running from the un-protected socket for non-critical stuff like battery chargers, document scanner, shredder and cordless hoover.
On the protected side, I have an HP Microserver, HG612, hard-drive box (8x WD RED drives), a pfSense router (Intel NUC thing), Raspberry Pi and a Netgear 8-port switch. That’s via a 6-way extension wired with a trailing IEC type E plug.
All that shows as 30% load and it’s reporting ~25 mins runtime at that load. Plenty of time for the usual kind of cuts we get.
I’ve got it connected via USB to my pfSense box which is running the apcaccess daemon. My server’s apcaccess client connects to that over the LAN so the server can be cleanly shut down on battery-low events.
Works really well and has been tested several times lately as we had an underground cable develop a fault that blew fuses at the substation several times.
Plus, we have a borderline out-of-spec supply here. Our line voltage is usually in the region of 258V, often going above 260V. It’s very reassuring to have all the protected stuff being fed a stable 230V!