Have you missed the boat for Pimco's bond ETF?

Bill Gross is the biggest star in the fixed-income universe.

And the $285 billion bond portfolio he manages, Pimco Total Return is by far the largest fund. But with size come restrictions, like the ability to move nimbly in and out of securities.

Enter Total Return ETF , launched in March 2012. With far less in assets, the exchange-traded fund, which you buy and sell like a stock, has returned 12.39% since inception, vs. 6.96% for the mutual fund version.

That success, though, has brought in a ton of new money, signaling it may be too late to jump on this bandwagon.

Growing pains

In an interview with Money, Gross admits even he was surprised how well the ETF did right out of the gate. Perhaps he shouldn't have been.

Early on, its small size let one of history's best bond investors focus on his top ideas -- the ETF holds fewer than 1,000 securities while the fund has over 20,000, according to Morningstar.

"Investors should know that the past few months probably won't be replicated," Gross warns.

Though the ETF is 1.4% of the fund's size, its assets grew 40-fold in less than a year,

The challenge of deploying all that at once explains why the performance gap is closing.

Since January, the fund has gained 0.33% while the ETF gained just 0.15%.

Says Morningstar analyst Timothy Strauts: "You will need to expect realistic returns."

An unpredictable ETF

Yes, you're betting on Bill Gross, but it's hard to know what you'll get.

Unlike other fixed-income ETFs, Total Return is not an index fund. On the plus side, that means Gross isn't "tied by the leash" of a benchmark, he says. On the other hand, you're talking about a manager noted for going against the grain.

In 2011, his Total Return Fund went from having almost no exposure to government bonds (including U.S. Treasuries) to a hefty 76% weighting -- all within a year in which Gross lagged his peers.

Today the fund's exposure to foreign markets such as Italy and Brazil is above the category average. So investors seeking consistent sector exposure should look elsewhere.

Making matters more confusing: The ETF weightings differ from the fund's, though Gross expects that to change going forward.

Deal or no deal?

Before BOND's launch, one of the cheapest ways to own Total Return was through its A-class shares. By comparison, this ETF is a bargain.

There's a cheaper way to buy Gross' skills, though -- through Harbor Bond , a Money 70 fund that he also manages and that charges expenses of 0.54%. Unlike Total Return ETF, which must be bought and sold using a brokerage account, triggering commissions, Harbor Bond can be purchased directly from the fund company.

Also, relative to iShares Core Total U.S. Bond Market , which tracks the same index Gross weighs his fund against, BOND is pricey.

Sure, you're paying for talent. But Gross isn't perfect. In fact, he underperformed his peers in two of the past four years.