Rating: 4 / 5
I used this app with 1:25K and 1:50K OS maps for a 5 week 2013 hike in Scotland. For the task of importing and displaying my gpx data on pre-downloaded OS maps, it was flawless. I don't know of any other apps that provide the current OS maps and have a better more usable feature set. For hiking in the UK (and maybe other countries in Europe), I believe this app is the best solution.
For maps of the US and Canada, I think Gaia GPS is a better solution, since it lets you use one app for both USGS/NRCan and Satellite imagery. Topo Maps is my favorite solution if all you need is USGS maps and waypoints (but no tracks), since it is so easy to use.