If you use Toppik for the hairline, make sure you also get the Spray Maximizer attachment. Otherwise it is very difficult to even attempt sprinkling Toppik so that it works how you want it to on the hairline.
Just my opinion, but look for the original Spray Maximizer(maybe on Ebay). I have both the original(looks like a old time perfume sprayer) and the newer version, which you just push down on it to work it with one hand. And I prefer the original sprayer, even though you have to maneuver it with both hands. I have found that it just sprays a finer mist of Toppik. And to me, it is just easier to control than the one hander, oddly enough.
But yeah, get a spray maximizer if you are going to put Toppik on your hairline.