Yes I can understand where you are coming from with that aspect of it, I am also an experienced pilot. What I mean is, I don't see the point in turning down the opportunity for interview experience with an airline... It will be fairly similar to any future airline interviews you have...
The argument in the post before you saying you could be applying to other airlines in the mean time, yes you could but right now airlines aren't currently rushing to anyones door looking to recruit you, the Stage 1 interview is 8:30 - 1300 in London, so it's half a day.. Don't see the point in turning it down?
If you get through then it's a free holiday in hong kong for you and if you're married your wife... That is I agree a bit more time consuming and could maybe understand you rejecting the offer to go there if work didn't permit but really don't see the point in turning it down.
Aswell you might want to consider that reading one thread on PPrune then deciding it's not for you is a bit hasty...
Tis up to you what you do at the end of the day, but hope you can somewhat see where I am coming from...