Why does Gold ETF offered by different companies varies in cost?

I fail to understand why price of Gold ETF varies across companies that offer it. Shouldn't the cost be same?

And it is safe to buy Gold ETF from one single Company? If not why?

It would be very helpful if anyone of you can help me with the answer.

Lookup Expense ratio

1. Gold ETFs not only hold gold bars, but also debt instruments and cash for some liquidity, so that makes a difference to the NAVs of the different ETFs.
2. Division of number of units will change per unit price. eg. 0.5g or 1g
3. Expense ratio: although this is very small

There are two types of ETFs: Active and Passive which changes how they are managed.

ETF's are supposed to "mimic" with a margin of tracking error.

ETFs will be tweaked to optimize returns, only then, will an investor be confident to buy it.
Else you can buy commodity MCX gold and sit tight.