Napisan Vanish, Sard oxy clean are all sodium percarbonate and do the same job.
They all contain Percarbonate, in various amounts, mostly something like 30%, balance is called filler in the chemical trade (granulated partly hydrated Sodium Carbonate). Trey are designed to get shit out of nappies, not to clean brewing equipment, if you think they will do the same job as made for purpose brewery cleaners, you are wrong.
Sodium Metabisulfite has next to no cleaning power, it doesn't even kill most bacteria, just shuts off their ability to reproduce. To get any effective sanitisation with it you need to make it up into a solution, wet the surfaces then let it air dry as it dries, it gives of Sulphur Dioxide (SO2) that is the sanitiser.
Remember it has a shelf life, I would break it up into small portions and store them in air and moisture tight containers. Otherwise by the time you get to the end it will all have broken down and wont be effective.
Same applies to the Perk, looses its Oxidising power over time, exposure to moisture in the air speeds this up.
Darren you say your an accountant. Work out what a brew costs you in both dollars and time.
How much proper sanitation costs.
How much you would risk knowing for a certainty that poor sanitation will cost you a brew or two in infection losses eventually. On the way your beer will probably get slowly worse and worse until its undrinkable. What usually happens is you adapt to the changing beer, by the time its undrinkable you will lose all your beer in stock and probably all or most of your equipment will be too contaminated to recover and need replacing.
Its one of those cases where being tight is its own punishment.
Mark