⭐ Merited by pooya87 (2)
That means they could decide that Bitcoin Diamond is the real bitcoin and reduce the price down to a fraction of a dollar and also sell the rest of the coins (bitcoin and the shitforks) and pocket the money with their investors having no right to any of that money 
So invest in the company that created the Bitcoin ETF instead of investing in the Bitcoin ETF itself 
Or do what they all try: create your own Bitcoin ETF.