If you're using the one-can 'budget' kits which require the addition of a kilo of sugar, then spraymalt will give you a better beer.
Sugar adds nothing to your beer apart from alcohol, and can make your beer seem thin. The sugars in malt extracts give your beer the alcohol plus some more body. It's not quite a like-for-like substitution, but instead of using 1kg of sugar you could perhaps try 500g spraymalt + 550g sugar.
If you go up to the two-can 'premium' kits, then you don't need to add sugar or spraymalt.
Sorry, I don't know the suppliers on your side of town.