Fantex Inc., a startup based in San Francisco, is now selling stock in the star NFL running back Arian Foster. Sort of. The company has created a subsidiary, Fantax Holdings, that will track "brand value" — a complex metric that includes performance, endorsements, earnings, and other factors — for professional athletes and other celebrities. And you, the fan, can buy in for $10 a share.

The announcement is being hailed as the first athlete IPO, but that’s not really what’s going on. Fantex’s celebrity trading platform is an innovative idea, but it’s somewhat tangential to the company’s real business. Fantex is primarily a marketing and "brand enhancement" company, and the trading exchange is basically a clever way to hook big name clients — albeit one that could be fun for NFL fans.

The "IPO" will raise $10 million from "shareholders," which Fantex will use to pay Foster up front. The athlete is then obligated to pay Fantex 20 percent of his earnings for the rest of his life. Fantex then has an incentive to help Foster build his brand and make more money.

Fantex will assign a brand manager to every individual it signs

According to a filing with the Securities and Exchange Commission, Fantex will assign a brand manager to every individual it signs. The company will "assist our acquired brands in increasing their value via technology and through leveraging our marketing, advertising and strategic partnering expertise." That’s the real business. The main difference between Fantex and other celebrity brand consultants is that Fantex is signing a longterm deal. The trading platform is just a gimmick.

Superfans may still be excited about purchasing a stake in their favorite Houston player, who also happens to be one of the highest paid athletes in the country. So, is Fantex’s Arian Foster "tracking stock" a good bet?

There are a few caveats. Fantex is positioning the deal as stock in Foster, but buyers are actually getting common stock in Fantex Inc. — and a very small amount of stock at that. All the Foster shares together add up to 1 percent of Fantex, which means Foster shareholders have no influence on company decisions.

So, is Fantex’s Arian Foster "tracking stock" a good bet?

The company also reserves the right to convert Foster shares into "platform common stock" at any time. That means if Fantex signs contracts with more athletes, your Foster shares could suddenly be converted into shares in Serena Williams, Usain Bolt, and David Beckham, or whoever else Fantex has signed with. You will also be required to sell your shares on Fantex’s exchange, not on the open market.

Fantex is not obligated to pass Foster’s earnings on to shareholders as dividends. Furthermore, you’re also taking on a huge risk by betting on Foster and on Fantex, a startup entering an entirely new business.

"This investment, then, is basically the worst of all possible worlds: if Foster fails, it fails, and if Fantex fails, it also fails," writes Reuters blogger Felix Salmon, calling the offering the "bad investment of the day."

Finally, the calculation of "brand value" is more complicated than it sounds. Fantex is getting 20 percent of Foster’s earnings, based on quarterly statements the athlete is required to file disclosing all his revenues, so you’d think the brand value would be tied to the amount of money he rakes in.

Instead, Fantex says brand contracts will be assessed at "fair value," which is the company’s estimate of what people will pay for them. For Fantex, that includes not just Foster’s earnings but also his estimated future earnings, age, attendance at games, "likeability," number of Twitter followers, and "personal drive and ambition."

"While we intend for our Fantex Series Arian Foster to track the performance of the brand, we cannot provide any guarantee that the series will in fact track the performance of such brand," the company says in its SEC filing.

"We cannot provide any guarantee that the series will in fact track the performance of such brand."

There are various new platforms that allow students and entrepreneurs to sell stock in themselves, but an athlete selling stock in himself is pretty new and weird proposition that that takes advantage of the recent loosening of securities laws under the JOBS Act. (Although, as Salmon points out, the concept has been around longer than Fantex would have you think.)

It doesn’t seem like it’s a very good investment, but it’s certainly good marketing.