I would not think for a moment that advertising in any
one UK mag is a good idea.
The most you will do is reach approx 1/4 of the people that actually read the UK flying mags, and a lot of pilots almost never read them.
The free mags might get about more.
GA Europe is one which I see lying around everywhere aviation-wise I go. It's also significantly European which expands the audience. For a higher value machine, I would also try the major US websites,
this one being just one.