pdath: I'd stick with a plain and simple low cost UPS if that is what you need. Ultimately you are going to need power for something else. Having the Internet up during a power outage is no use if you don't have a computer or something else to plug into it.
That was my original thought too. Many people access the Internet on their mobile phones and tablets, and those also keep running during power cuts. It makes sense to power the router (and ONT for fibre) using a more efficient DC-DC power supply if you can get away with it, and it's a lot cheaper than buying and maintaining a real (good quality) UPS.
My unit arrived yesterday, however I'm still waiting on my supplier for the battery (hopefully this afternoon). I won't be using it to run my router (on my UPS), but a remote low-powered computer.