Wow, what a crazy blast from the past.
Personally I would rather own physical metals than buy an ETF. That's just me.
The US Govt issued 'Silver Certificates" (ie paper money with blue colouring) because they couldn't dig enough silver out of the ground quick enough...
Without having the OP to read, it sounds like they have a quantity of Silver and issue certificates in their stead. The only problem with that is if they were to then lend the silver as part of a loan guarantee (or indeed sell it at a price peak hoping the market then goes back down). The trouble would then be should investors want to reclaim their funds (silver) only to find the cupboard is empty.
Plenty of Banks went bust in the 1880's - 1920's through this kind of nonsense.
When ever there was a run on silver, people would go to the banks to collect silver dollars until the Govt one day said "no, you can't do that any more." A couple of years ago, a mid west bank discovered it had $1M in silver dollars sitting in bags at the back of it's vault - the dealers who they contacted to arrange to sell to the public agreed to trickle feed them out so as not to flood the market, but you guessed it, one got itchy fingers and dumped his share.
That's not to say this trade isn't kosher mind you, just a little history lesson.