Like tinaf1 I have tried Wunderbrow - also paying about £20 for it. I also use a much finer brush than the one supplied to apply it. I really like the product and it does stay on well - left it on overnight to see, once - however I am disappointed that the manufacturers don't make an ash blonde shade - the Blonde is far too yellowy for my skin and hair colour which is silver white. I have written to suggest an additional shade, but didnt get any response! Shame as if I could get it in a silver grey or ash blonde shade, I'd be a lifelong customer without a shadow of a doubt.
Not sure about the tattoo route - we need such delicate definition as we age that the photos I've seen of people who have had that done, rather put me off, as they look so severe and unnatural!
Wunderbrow really is great if one of the four colours suits you and you swap the brush for a finer one. I also use an old dry mascara wand to brush over the browline after application of the product as that not only tidies up the few actual hairs I have left, but seems to prevent the product being too thick. 