Guy, Outdoor Active does some of what you want.
I cannot find if it has off route alarms at all. Maybe others on this forum have discovered how to get that.
Not too sure if it has the speed displayed the way you would like it to be.Again maybe others have worked this out.
All other points are covered. Their TOPO maps are good. Not sure if OS maps are actually needed when you can download satellite and Open source maps for free. I always carry a paper OS map anyway. Though recently gave been questioning that need.
I think the simple navigation format of Viewranger is something they are really poor at, and hopefully that is why they bought out that team, to improve their offering in this respect.
As an app it is as much a "community" thing as much as anything. They have some great routes, probably a lot ported over from VR. There does seem to be more interaction between the app users than VR, which is good if you want but not what I'm after. I'm going to keep using VR until the death then I'll purchase a Garmin of some sort, probably an Etrex 20. Unless if course Ourdiir Active improves its navigation offering,
Oh, and it's help page.