I have used this set several times now, and also different Sets (Set 1 is for light blonde hair, but there are others for darker hair and there are extra lightener sets).
I have always been very pleased with the results, beautiful light blonde highlights that stand out but don't like fake, non-brassy. The set comes with a little brush (a but like a mascara wand) that you can use to easily brush on highlights. I have used the brush but also my gloved fingers to apply it, both ways work beautifully.
That said it can be helpful to have a friend to help with applying highlights at the back of the head but its not a must.
I have only ever seen the set being sold in Germany (in just about any drugstore) where it's very cheap (4 euro) and you get a lot of product so you can really apply loads of highlights.
I wish it was more widely available because it is easy to use and cheap.