Hey Adam
Always happy to help.
With regards to harpic toilet cleaner, I have not found anything as quick as this and for that corner gunge and limescale just leave on for a minute and just scourer out, it really is easy and it won't damage the stainless steel if you leave on for 1 min, rinse off with the shower attachment and wipe up and buff with kitchen towel, job done.
With regards to below water brown limescale the only thing i use here is half a bottle of spirit of salts (£2-3) pour in slowly (hold breath) close lid, go back at the end of the clean and brush away all the limescale, flush and it's done, used it for almost 7 years and it never fails but just be careful it's highly toxic & pungent.
The best degreaser I have used and again for almost 7 years is brillo degreaser in 5ltr tube and dilute down into trigger bottles, it will literally melt the grease in front of your eyes, also nicotine.
With regards to the steam cleaner, on limescale about as much use as a 3rd armpit, but to save time on skirtings, windows, tiles, kitchen units it is fantastic.
A couple of tips:
You know that blue/green limescale build up in baths and sinks from a dripping tap? squirt a splodge of harpic on it, leave for 2-3 mins while you do something else, then scourer off and it just goes away, easy
BIO-logical washing liquid (Persil) now, you want an all round phenomenal degreaser NOTHING beats this, it is AMAZING and smells great. It's sole purpose if to break down fatty deposits and protein based stains. Some times you can use it neat (I did this today on a kitchen blind and made short work of it) i usually dilute 1/2 a cap into a 500ml trigger spray.
Regards
Martin