From my ios11 iPad Pro I downloaded and tested w Speedtest app. Download speed: 81.9 mbps, upload: 8.48 mbps. It’s close to what they promise of 100. Is 81.9 close enough from my iPad Pro?
Is it enough, sure. Is it the best you can do? Not if it is less than your ISP service level. A newer router will be more likely to hit the speeds you are paying your provider for. Not to mention being more stable, not losing settings, etc. If your service is cable, you might actually reach 110-120 Mbps speeds as cable companies advertise "average" speeds and tend to overdeliver a bit to offset the occasions when speeds my be less.
My cable company has regularly increased my speeds over the years, without changing the service tier or price. So, a new router, while being more stable\able to recover after power hits, would tend to be a future proof strategy as well. Your provider is unlikely to let you know if your equipment is inadequate unless you call service to troubleshoot speeds. Then, they will likely try to sell you on upgrading to one of their modem\router devices for a $10-12 per month fee. Buying your own modem and router will often pay for itself in a year or so compared to the rental fees.
That said, depending on what you do with WiFi, streaming, etc, the 81Mbps is adequate for even 4K content. The most likely scenario where you might notice a difference is downloading large files to a Mac\PC.
Back to your original post. You should never have to restore to factory settings, these are often inadequate security out of the box. When you configure a WiFi router, there are a few things you always want to do to protect yourself from outsiders. Don't forget, your WiFi devices often store a lot of sensitive data. The typical things are router admin password, whether or not it allows configuration from the WAN (outside your home network), Network name and security\password. If these are default, chances are the defaults are the same as others with similar routers and this allows strangers to get on, or configure your network, access your data, etc. So, if the router loses configuration on unexpected reboots, you are either leaving yourself vulnerable, or having to deal with a lot of complicated configuration each time. A newer router would probably eliminate this risk.