Before deciding what to use on the shower block you need to decide what you are trying to do.... remove Mould, Scale, General Soiling and on what surfaces.
Then if in doubt, pop along to a good cleaning product supplier and get some advice from them, maybe even a couple of free samples.
Never be afraid to ask their sales rep to pop along and have a look at the job with you. Most are pretty obliging and you gain more knowledge at the same time.
Not wishing to be disrespectful and hope it helps.
Les