I grew up and spend a large part of my modeling using them, there was nothing else available back than and back home.
Now I use Gunze(mostly) and Tamiya, Humbrol is available over here but not in all shops.
No problems with the paint except it is way too thick, and you need to seal the tins tighly to prevent the thinner from evaporating.
For thinning & cleaning I have alwasy used Mineral Turpentine (evil smelling stuff).
Overall the paint is good and will cover well, very similar to the Revell colours. Their Metalcote paints are not too bad either.
At times I wills till buy a tin here and there for a specific colour that I want to use (Coal black, etc.).