When big name U.S. hedge fund managers disclosed their fourth-quarter stock holdings last week, a couple of exchange-traded fund companies took particular note.

Global X Funds and AlphaClone LLC both offer ETFs that mimic the stock picks of high-priced hedge funds. When the hedges publish their long positions, these companies jump in, making sure the same holdings are in their much more affordable ETFs.

This approach won them outsized returns in 2013 and has emboldened expansion. New York City-based Global X already plans to launch two similar funds in coming weeks, as soon as they clear regulatory approval.

"If you know what every large investor in the U.S. owns in his portfolio on a quarterly basis, there is value in that information," said Global X head Bruno del Ama.

The Global X Guru fund was up 47 percent in 2013, a year when the average hedge fund returned 9.3 percent. San Francisco-based AlphaClone's Alternative Alpha ETF gained 36.12 percent.

But it is not clear how such funds, which benefited from a strong stock market last year, will perform in more volatile or down times, when hedge funds might be expected to fare better.

The ETFs build their stock lists from the 13F reports that hedge funds must file with the U.S. Securities and Exchange Commission 45 days after the end of each quarter. The hedge fund therefore buys a stock much earlier than the ETF and does not generally disclose why it did so or how long it plans to hold the investment.

By the time an ETF has bought a stock, the hedge fund may have already sold its position, or the shares may have moved up substantially from the hedge fund's purchase price.

Furthermore, the Global X ETFs are designed to use only a part of the hedge equation: buying the long bets of a carefully constructed portfolio without protective hedges like short positions in offsetting derivatives.

"What you end up with is a fairly different entity" from a hedge fund, said John Rekenthaler, vice president of research at Chicago-based Morningstar. While an ETF is low-cost, liquid and transparent, "you give up quite a bit when you're looking at filings, which is old information, and long-only information."