no difference.
I have been colouring my hair for years, it's probably all grey now under the chocolate brown.
I have shoulder length, layered hair.
the application is important & it gets easier with practise!
buy a plastic, hair tub & brush set, pound shop have them.
start at hair line , especially if your grey, then work along the hair parting , sectioning down each side, ask for help with the back if necessary, but perfectly possible to do it yourself.
if you always use the same colour , then the roots are easy to do, just mix half the mixture, This will give you 2 root applications from one box.
I have tried all makes, believe me, there is very little difference, apart from the price.
I tend to use Aldi's own make or the pound shop one now.
I have at times had a colour at the hairdressers, as a treat or if there was a good offer on. No one noticed the difference to my usual home efforts!
Good luck.