Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you're a fan of investing guru Louis Navellier, and are interested in investing in the 100 stocks that his quantitative system deems to be of the highest quality in the U.S. market, the RevenueShares Navellier Overall A-100 ETF (NYSEMKT: RWV) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously. In fact, the ETF aims to outperform the index.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The RevenueShares ETF's expense ratio -- its annual fee -- is 0.60%. The fund is fairly small, too, so if you're thinking of buying, beware of possibly large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF has underperformed the S&P 500 over the past three years, though that's not really sufficient time period over which to draw strong conclusions. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

Why this ETF?
You should like this ETF if you're bullish about the index on which it's based: the Navellier Overall A-100 Index. The ETF differs from it by weighting its holdings by revenue, not market cap. It's also rebalanced every quarter so that it's based on fresh revenue data. Navellier has had his financial successes, but still, there are reasons to be cautious about the ETF, such as its specific stock selection method being in a bit of a black box.

More than a handful of companies that have been in, or are in, this ETF had strong performances over the past year. Green Mountain Coffee Roasters (GMCR.DL), for example, more than tripled in value, despite patent protection running out for its K-cup design. Part of its success is tied to its Keurig machines, and to savvy partnerships it has forged. It's also poised to profit from its coffee costs falling, as that can quietly boost profit margins. The coffee market keeps growing, but private labels are giving name brands a run for their money. Green Mountain's recently reported third quarter featured GAAP EPS up 65% over year-ago levels, and revenue up 11%.

Gilead Sciences (GILD -2.65%) more than doubled, with investors optimistic about its oral Hepatitis-C drug sofosbuvir, which has cleared four phase-3 trials and received priority-review designation from the FDA. (Some think its sales might approach $6 billion annually.) The company is well-known for its success with HIV drugs, though competition there is growing, and it faces some patent expirations in coming years. The stock may not look like a bargain, with a P/E ratio in the 30s, but its five-year projected earnings growth rate is steep. Its second quarter featured product sales up 14% over year-ago levels.

Flowers Foods (FLO 0.04%) surged 76%, enjoying accelerating growth rates for revenue and earnings. The stock yields 1.4%, and its dividend has been steadily growing in recent years. With a forward P/E ratio near 21, it doesn't appear to be a screaming buy, and it has a debt load to consider, as well. It has been making some savvy and powerful acquisitions, though, such as Sara Lee and Earthgrains brands in California, Wonder Bread, and a high-profile $355 million purchase of some Hostess brands, such as Wonder Bread (but not Twinkies). As analyst Stephen Simpson has noted, the company's scale and efficiency are improving. In Flowers Food's second quarter, volume grew 22%, revenue jumped 32%, and net income surged 64%.

Amgen (AMGN -1.29%), the biotech giant, jumped 29%, and yields 1.8%. Among its many offerings is arthritis drug Enbrel, which is the third-highest-selling drug, generating $4 billion in revenue in just the first half of 2013. (Amgen shares those gains with partner Pfizer.) The company has a bunch of promising "biosimilar" drugs, but along with its peers, seeks more clarity about them from the FDA. Bulls see promise in its pipeline, and with its forward P/E ratio near 12.5, many think the stock is a bargain these days. Amgen has reportedly been looking into buying cancer-specialist Onyx Pharmaceuticals.

The big picture
A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.