I used to go to get my brows threaded at BB. First time was amazing and loved it, second time I didn't like it at all, and it was £2 dearer Their brow pencil is quite waxy and gives a delicate "natural" finish vs the big brow that's in fashion now - at least for me.
I now use the L'Oreal Super Liner Brow Artist Plumper, which is like a mascara wand. It's amazing. But for sparse brows, you might want a pencil/powder if you want to fill them out.