Having been involved with several of these, I can report fairly accurately.
It is a lottery as to whether you will get a good view, however, if the operator is good ( sorry, blatant plug - we are ! ), they will allow sufficient time to get north of the Faeroes where you should get a good view if the conditions are suitable.
There are several websites that offer projections as to the location of the Auroral Oval - i.e. how far south the Aurora are visible. This depends on how active the sun is as the Aurora are a result of high energy particles emitted from the sun interacting with the Earth's magnetic field which is concentrated around the poles.
So, armed with the space weather forecast, we set off - the flights are always timed so there is no moon present. Usually there are 2 astronomers on board, they give a running commentary of what is visible in the sky - star wise - and also a comprehensive talk about what the Aurora are and how they change in colour and appearance.
Once up in the area, I personally try and organise a 20 minute free manouevre window from Scottish or Iceland which is usually granted. Then 2 mins East, turn North, 2 mins West, turn North gives everyone a good view before it is time to return.
All legal lights are doused so the pax get as good a view as possible, seats are changed, no flashguns allowed (they check before we get up there !)
I have done 4 or 5 of these flights and we have seen aurora on all occasions, in fact the operator we flew for had done over 30 and had only had 2 failures.
If you get chance, try one of these flights, they aren't dear, the information is very interesting and you get a chance to see one of the most wonderful sights of the night sky.