Hello,
I have an account with CornerTrader.
Yes, you can buy ETFs through them and in my opinion the selection of ETFs offered is sufficient to build a diversified, global portfolio. For example, all iShares Core ETFs for major regions are offered. It’s possible that not all of them are available, but I can find all of the ones which I am interested in.
The only disadvantage in my opinion is that available ETFs aren’t listed in their own category in the trading platform. You have to search for them using the search tool, which means you have to know exactly which ETFs you want (i.e. iShares Core MSCI EM IMI UCITS ETF). I can’t get an overview of all available ETFs, even if I search for “ETF” in the search tool.
You can find information on ETFs on sites like justetf.com and get the exact titles so you can find them with the Cornertrader search tool. All in all it isn’t too complicated. Once you have found an ETF you are interested in, you can add it to a watchlist (you can create watchlists yourseld in Cornertrader).
Why not try opening a demo account to see whether it works for you before you commit?
Anyway, I hope my input helps somehow.