The trouble is VR’s indigenous mapping is not great quality and there is now no way to get better mapping by subscription. OK if you are a follow the line on the screen kind of walker but less helpful if you want to know which side of the hedge line you should be on.
Also, I believe the useful safety feature, Buddy Beacon, has also transferred to OutdoorActive.
To get OS mapping from OA is £2.50 a month, cf the price of an OS app subscription of £23.99 with auto renewal or £3.99 a month. It really depends on how you value the other features. OA will record a trace while following a route, with the OS app it is either or. The OA user support is really on the ball, the OS, less so.
On the other hand, if you have all the maps you need from past VR subscription, stick with it while they last then decide.
As to other apps, such as Backcountry, I have no experience so cannot comment.