I don't think it's that risky, but one risk inherent in the strategy is that it doesn't provide broad diversification. It's a controlled growth strategy.
Markets go up more than they go down. But it's been a ruthlessly declining stock market, so the funds have gotten their day in the sun.
We're not exactly sure why, but one possibility is although people are discouraged by the performance in the market recently, there may not be a lot of fear. It may be, despite the slide, that there's still a large degree of optimism in the market.