This is the electronic way of investing in silver via the stock exchanges. It's basically a fund that invests in pure silver. Its price tracks the international silver price.
Here the purity is assured. The gain/loss in physical silver, will be closely matched in the silver ETF. You also don't need to worry about storage and safety.
Be mindful of the cost of the silver ETFs in the form of the expense ratio of the fund.
You will need to carefully select which silver ETF to invest in after considering factors like expense ratio as well as the tracking error. The tracking error is the difference in the movement of the physical price and the ETF price.
To know more about why silver ETFs are a good choice, we suggest Vijay Bhambwani's video - Silver ETFs: A Shiny New Investment.