I bought it yesterday but can’t work out what the little piece is on my photo? Also it’s meant to have an abrasive sponge to remove the rusty bits of paint etc but it doesn’t feel very abrasive

That is for chips to smooth the edges before dropping the paint in. TBH it's not the best and very watery so be careful.

10 minutes ago, F0CUE said:

That is for chips to smooth the edges before dropping the paint in. TBH it's not the best and very watery so be careful.

Ah right lol. It just feels like a piece of plastic, doesn’t seem like it would smooth chips. I only want to do a chip on the bumper where it meets the arch and I’ll do a load of stone chips on front bumper. Does it not match very well then generally?

It's just not very easy to get right but with a bit of patience although my last car was moondust silver so was hard to get right. here is the instructions 

Simply use the special glass fibre prep tool to remove any loose/flaking paint and all rust from the chip or scratch. Then apply the high build primer filler using the precision nib applicator or brush into the prepared rust free chips and scratches, building up the thickness in stages (leaving 10-20 minutes between coats) leaving 24 hours to harden.

Lightly rub down using abrasive side of special tool to achieve smooth finish, then apply your colour match using the precision nib applicator or brush to the prepared and primed chips or scratches. Build up the colour in stages by leaving 10-20 minutes between each coat*. Leave the paint for 24 hours to harden then simply buff the surface using fabric side of special tool to blend in the repair.

Assume you don’t get a brush with it and have to just squeeze the pen onto a brush?

Unscrew the lid the brush is inside.