Most expensive cleaning products are a total waste of money.
We have very hard water here which causes horrid marks on both the loo and any stainless steel.
Most stainless steel can be brought up to a lovely polish just by using white vinegar and a cloth to polish it off. Works a treat on taps and draining boards too. Do not use on ceramic taps or basins.
For the toilet I have tried all the expensive products but the best thing I have found is 19p Morrisons bleach for 2 litres (I am sure other supermarket own brands will be just as good) and a good hard toilet brush. Leave the bleach in the loo for as long as possible (over night if possible and if you have good ventilation) then give a good hard brush. This is normally enough to get rid of any limescale and leave your loo looking like new!