Ok who to answer first, let's get Rogers gripe out of the way.
I support the truth, not the pool industry per se.
Pool salt is different because it is stabilised so conatins cyanuric acid stabiliser. Have you read my post on "Opening up for the new season" It gives a breakdown on why you need cyanuric acid stabiliser but too much is bad.
The crime would be paying extra and not recieving what you paid for. If your pool has a good level then of course you should avoid stabilised salt and use water softener salt providing it's pure enough.
I have seen stabilised pool salt from €9 to €12 a sack so not that much of a rip off, of course if you don't need it don't use it.
Packaged products, I am not a fan of, the multi action gallets and choc used widely contain cyanuric acid stabilser in quite a large proportion around 60% is stabiliser so after a seasons use (assuming you started at zero) your pool will contain more stabiliser than you most likely need and by the time you start next season you will begin to loose control of your pool so end up draining a reasonable amount of water out and replacing it with fresh as cyanuric acid happends to stay in your pool unlike the chlorine. Calcium hypochlorite doesn't contain cyanuric acid but does contain calcium to slow down the disolving of the tablet so in some hard water regions that would be a poor choice to.
Anti algae really isn't much use, save your money, if you have an algae problem then chlorine works faster anyway. It actually get re labelled and sold as Hivanage, they probably sell more of it then. Over winter when the chlorine level drops to zero there maybe some small benefit as a safety thing but I don't use it. The winter cover should keep out the light so alage doesn't grow and the temperature falls so alge doesn't grow much then either and in the spring just chlorinate, maybe choc with liquid chlorine NOT choc.
pH + and - are the same throughout so it doesn't matter who's you buy, just buy the cheapest.
On to alternatives,
The best way to chlorinate your pool is with liquid chlorine, use javel from a brico at around €18 for 20 litres. It has 9.6% active chlorine so you add 100ml for every 10m3 of your pool size.
pH - hydrochloric acid again from a brico about the same price as javel. around 200ml for each 10m3 of your pool size to reduce the pH by around 0.2 (it is difficult to be precise as it depends where your pH is to start with, the higher it is the more you will need to bring it down by 0.2 as the pH scale is logarithmic not linear but you'll soon get used to it and the savings! Be careful with acids, they burn and fume so goggles and gloves are advised.
NEVER mix chlorine with acid it may kill you!
pH+ is soda ash, buy the cheapest.
Alkalinity, that's bicarbonate of soda, buy the cheapest, 900grms will increase each 10m3 alkalinity by around 50ppm.
That is about all you need in your pool to look after it, no magic stuff although there are some cases where additional products can be used like flocculents/clarifyers.
Never add concentrated chemicals into a skimmer, always dilute where necessary or disolve in a bucket of pool water before sprinkling or pouring around the pool in front of the returns when the pump is running.