I've learnt from this great forum to be very, very skeptical of pool shops and their unnecessary products. Had a look at Bunnings (big warehouse type place in Aus that sell everything including pool chemicals).
Just a question out of interest - product called Pool Shine. It's 450g and the active ingredients are 450g/kg dichlor (so 202g in this) and 100g/kg sodium tetraborate pentahydrate (ie Borax!), so 45g of it. Claims to 'assist salt water chlorinator'. I've read in detail here about how Borates can help, but surely this tiny amount wouldn't make any difference? 45g of that according to PoolMath provides about 0.18 ppm for my size pool!
I'm sure there are suckers out there who'll buy it and many others though.