I've been using root touch up sprays, mascaras etc and they're great if you only need them for a few days, for what I've done with my hair I needed something more permanent.
This is the perfect solution. It lasts about 3 weeks and is super easy to apply. The colour and developer bottles are easily resealed and the brush is easily cleaned dried and stored back in the box. I even use the plastic the brush comes in as a reusable dye tray.
As well as being compact and easy to use, the shade really does match my hair (which I was a little bit skeptical about), so it's also seamless.
I will be using this product for a long time.