Bill Ackman is one of today's best-known investors, and many everyday investors study his investments in an effort to mimic his success. Until recently, Ackman's hedge fund was limited to people who could invest a significant amount of money. But now, Pershing Square Holdings is a publicly traded investment, allowing everyone to invest with Ackman.

Should you invest with Ackman?
Ackman's Pershing Square is an activist investor. Unlike other funds, which simply invest with the hope that shares will increase in value, Ackman actively pushes for change at companies Pershing is invested in.

His aggressive approach to investing has yielded a history of both successes (such as the General Growth Properties turnaround) and failures (such as his activist push at Target). Today, Ackman continues to swing for the fences with such high-profile investments as Fannie Mae (OTC:FNMA), Freddie Mac (OTC:FMCC), and Allergan (UNKNOWN:AGN.DL).

Pershing Square is not a conservative fund. Although it holds a variety of investments, investors should note that Pershing Square is only for investors with higher risk tolerances due to Ackman's "swing for the fences" approach, which causes additional risk and volatility.

Now Pershing Square is a publicly traded investment that lets ordinary investors track Ackman -- for a cost, of course. The investment has a 1.5% annual management fee. This is higher than that of most ETFs, which generally carry an expense ratio of less than 1% and no performance fee, though it's more reasonable when compared to the fees of managed hedge funds.  In addition to the management fee, there is a performance fee that could be as high as 16%, varying by sources of investment in Pershing Square.

By comparison, the longtime standard for hedge funds has been two and 20 -- that's a 2% management fee and a 20% performance fee. More recently, The Wall Street Journal has noted that the average has fallen to a 1.6% management fee and a 18% performance fee -- both still higher than Pershing Square's fees.

What investors get
Normally, I'm not a fan of managed funds, given that they've collectively trailed the market every year since 2008 and come with extra fees. But despite some similarities to managed funds, I think Pershing Square is worth a look.

Unlike many fund managers, whose performance is based on good stock picking, Ackman takes an active role in his investments and tries to squeeze more returns out of them. So rather than taking a passive stock-picking approach, Ackman is also conducting a business that is generating returns.

But as Bloomberg notes, the fees can add up over time. Pershing Square posted a gross return of nearly 1,200% since 1991, but returns for investors were reduced to 627% after fees. In exchange for the fees, investors get to benefit from Ackman's investments before they're made public.

Many of Ackman's investments -- including Zoetis (NYSE:ZTS), Fannie Mae, Freddie Mac, and Allergan -- experience a pop in their share price once Pershing Square discloses ownership, so investors who try to copy the investments from announcements and filings will find themselves missing out on the pop. However, these investors also miss out on the fees.

In deciding whether to buy Pershing Square Holdings itself or to just follow Ackman's investment reports, there is one more wild card: the possibility that Ackman could take on a non-publicly traded investment through a full acquisition or special investment class such as preferred stock or warrants. If this happens, trackers of Pershing Square wouldn't be able to copy the investment, and only Pershing Square investors themselves would see the benefit.

Around the time of the Pershing Square Holdings IPO, Ackman discussed taking a "decent-sized stake" in an American company, according to Bloomberg. Now that Pershing Square has raised some permanent capital through its IPO, it has more flexibility to pursue longer-term investments and even full acquisitions. Investors should note that full acquisitions would have been more difficult before the IPO, as Pershing Square's investors could withdraw funds at any time and force the fund to liquidate investments.

The portfolio
Pershing Square continues to hold a significant amount of Allergan shares, though Ackman has pushed for a sale of the company, which has now agreed to let Actavis acquire it. But because the deal has not officially closed yet, Allergan remains Pershing Square's biggest holding at 35% of the fund's portfolio -- nearly twice the weight of the next-biggest holding.

Other major investments include Canadian Pacific Railway (NYSE:CP) and animal health company Zoetis, both companies in which Pershing Square has become a member on the board after pushing hard for influence. In both cases, Pershing Square is sitting on a handsome profit after gaining board positions.

But perhaps Ackman's most interesting investments are in government-sponsored enterprises Fannie Mae and Freddie Mac. Ackman recently called these the "best trade ... in capital markets" and owns nearly 10% of each company. Ackman is one of many investors pushing through the courts to overturn an amendment in the preferred-stock purchase agreement that currently funnels all of Fannie and Freddie's profits to the Treasury.

Investing with Ackman
Bill Ackman has plenty of followers, but the IPO of Pershing Square Holdings finally gives investors the opportunity to directly take part in his success (or failure). But fees need to be taken into consideration, and investors simply looking to duplicate Ackman's current portfolio may be better off investigating the investments listed in his 13F filing.