How to identify the long term value of an EFT?

I started working with a broker a few months ago (I know, not the greatest timing but it’s what it it).

She’s picking EFTs and I want to know how to identify their long term value. Like, OK, now they are dropping, but what returns can I expect in 20 or 30 years?

I’m checking historic returns online, but I wondered if you could recommend me a) metrics and b) sites that offer those metrics in an intuitive manner.

Thanks a lot Reddit community!