The main reason Lithium hypochlorite (It is also the most expensive form of chlorine you can buy so it generates a lot of revenue for the pool store!) is recommended for vinyl pools is that it dissolves instantly when compared to the other non stabilized powdered chlorine , calcium hypoclhorite. If you put cal hypo in powdered form in a pool some of it will most likely sink to the bottom undissolved and can cause liner damage. (which is why it is recommended to pre-dissolve it!) If you are using liquid sodium hypochlorite you do not have this problem. Sodium Hypochlorite is sold in pool stores (Usually in 6%, 10%, and 12.5% concentrations as liquid chlorine or liquid shock. It is sold in grocery stores as liquid chlorine bleach (5.25%) or ultra bleach (6%). These are all exactly the same thing except for the concentration and therefore how much you have to put in to get a given chlorine level. The other ingredients in it are mostly water and a small amount of sodium hydroxide which is what keeps the chlorine in solution.

a far as the other 'damaging chemical substitutes' look at this example:
Alk increaser is labeled as either sodium hydrogen carbonate or sodium bicarbonate on the ingredient list. They are 2 different names for exactly the same chemical and what you get in the pool store is usually technical or commercial grade which mean it has impurities in it. You can get USP grade (means pure enough for food and drug use) sodium bicarbonate at the grocery store for less money as "baking soda"!

Hope this lays any fears you have to rest! The advice you will get here on the forum and on the sister website www.poolsolutions.com is probably the best pool advice you can get anywhere!