After having various forms of investment: "C" and others outside EK for over 7 years, all I can say is that "C" works for me.
I don't see the money, have no access to it, as it goes straight into the selected fund. OK, I might be paying a bit in fees for their services, but when we talk about other investment vehicles, in most cases we end up paying service charges, account management fees, money transfer fees, etc.., not to mention hidden ones. Yes, I agree, it doesn't give you the greatest choice of funds, but it's simple, safe and judging by returns is actually doing pretty well. Most of American equities funds made in the vicinity of 70% + in the last 3 years.