I thought if the currency is "strong" then you have a better chance of profiting?
The only way you have a better chance of profiting in anything is if you are in control. Meaning, start your own company.
Someone also mentioned ETF (I don't understand this) but in an article about the site it says that Betterment handles ETF:
"Betterment will build you an efficient portfolio comprised of widely diversified, low cost ETFs. If you don't want to manage your own portfolio, or hire a financial advisor, Betterment is tough to beat for the very low price."
If you don't understand it, never get involved in it.