Today is the day everyone can begin buying and selling shares in Robinhood, which goes public on the New York Stock Exchange after raising $1.89 billion in its IPO.

Why it matters: Robinhood is considered a proxy for the rise of retail investing, particularly among younger Americans. But it also has drawn regulatory and political scrutiny for a variety of business practices, and found itself in the crosshairs after users drove up the price of GameStop stock earlier this year.

The bull case: Robinhood has become synonymous with mobile, no-fee trading of stocks, options, and cyptocurrencies. Its business is booming.

• Revenue soared more than 300% between the first quarter of 2020 and 2021, hitting $522 million. Annual revenue in 2020 was $959 million, up from just $277 million in 2019.
• Robinhood isn't just taking market share from traditional brokers, many of whom have aped its no-fee model, but it also is growing the market itself. The company claims that over 50% of its users are first-time investors, and that its median customer age is just 31 years-old.
• It's also is benefitting from increased interest in cryptocurrencies, with Robinhood's crypto under custody growing from $414 million at the end of 2019 to $3.53 billion at the end of 2020.

The bear case: The risk factor section of Robinhood's IPO filing is a whopping 75 pages long.

• Some of it is pretty standard for a fintech where asset and data security are paramount.
• But lots of it is very specific to Robinhood, which is the subject of class action lawsuits tied to this past winter's meme stock trading frenzy and regulatory lawsuits over alleged securities law violations.
• Regulators also are probing employee stock trades and the fact that Robinhood's co-founders aren't registered with FINRA, Wall Street's self-regulator.
• Robinhood's primary revenue source is from something called payment for order flow, and there's been some political and regulatory movement toward limiting or even abolishing the practice.
• Then there's the volatile world of crypto, with much of Robinhood's increase tied to the particularly speculative Dogecoin.

IPO details: The company sold 52.37 million shares at $38 each, at the lower end of its proposed price range of $38-$42. It will begin trading later on Thursday under the ticker symbol "HOOD."

• Robinhood said it would set aside up to 35% of shares for its customers, although we don't yet know the ultimate percentage.

The bottom line: 2021 has been the year of the retail investor. By this time tomorrow, we'll know more about how the market is reacting to that reality.