Considering you say you are new to drones, you have successfully identified two very significant basic requirements, RTH (return to home position, which requires gps positioning, which in turn greatly improves the drone’s stability, hovering abiltity, and course holding) and camera view monitoring through a smartphone app (though some DJI controllers come with built in screens), You’ve already sussed that the sort of cheap drones advertised on Amazon or Temu are not worth bothering with; I didn’t, and wasted cash, and (more importantly) time on them. They are next to impossible to control accurately and the cameras are pathetic.
The mini 4K is a superb piece of kit and excellent value for money, but a few subtle inquiries with your lad about what he wants from a drone might be worthwhile before committing. I’d have at least a look at the DJI Neo; not as good a camera or gimbal as the 4K, smaller, lighter, shorter battery time, and not as adept at handling high winds, but a very capable and flexible little drone all the same.
The bare drone retails at £189, but does not include a controller at that price. It can easily be hand-launched and be flown without even a smartphone by pressing buttons on top, which will enable it to perform set manoevres which are ideal for vlogging and selfies, and can be controlled for more freestyle and complex flying by an app on a smartphone. Spending more and buying the one of the various RC controllers it can be paired with will enable it’s full flying potential to be realised, and it has comprehensive obstacle avoidance sensors, so is particularly good for indoor flying, ‘follow me’ on mountain bikes, and that sort of thing. It also has a propeller guard bodyshell, which means that minor collisions with obstacles are more survivable.
It is worth buying the ‘fly more’ drone packs, which will give you 2 extra batteries, a charging hub for them, and a carrying case. Budget for DJI ‘Care Refresh’, which will provide a replacement drone if anything bad happens to yours, well worth it, a set of lens filters if you are going to be doing serious photography with it, and a propeller holder (these are cheap but very useful, stops your props flopping about and potentially being damaged in the bag).
£400 should get you a pretty comprehensive set-up, but budget another £400 because it is almost certain that you are going to want a drone for yourself, and then you can race them…