I think £17 for a scenery of this level of detail will be worth it to some and not to others. If you like flying business jets and want to use Farnborough as a base, it’s a no brainer. If you live nearby, it’s probably worth it too. But if you’re only going to visit once or twice, then yes, it is a bit steep for that. There are larger airports available for a lot less, but I suspect this is partly due to their popularity - Farnborough is never going to sell in the volumes that, say, Zurich or O’Hare might, so I guess the developer has to charge more to make a similar profit. It’s a niche product compared with many.
But this is why I make a point of not mentioning prices in a review unless I either think something is a rip-off, or not that great but worth it because of the cheap price. Some people will consider £17 extortionate for Farnborough, others will be really blown away by the details and know they’ll get a lot of use out of it so will consider it very reasonable.