It depends on what you mean by a commercial radio, and who "the general public" refers to. There really is no single answer to the question due to the nature of how radio came about and grew. It didn't start on a given date and with a "first" radio receiver.
There were plenty of radios that were factory-built before that Atwater Kent mentioned above. By the way, it is hard to tell from the photo, but that set appears to be a Model 10 or one of its variants, from 1923-24, not from 1921.
Before about 1920, entertainment broadcasting was experimental and spotty, often transmitted by amateurs. Most transmitting was in code by amateurs and commercial communications and military services. While there were plenty of homemade sets built, factory-built sets were available back then. Some were crystal sets, some used a tube or two.
In the United States, all amateur activity was stopped during WWI. At the end of the war, there was a flurry of activity of amateurs getting back on the air, and commerical entertainment broadcasting started up in the early 1920's. As interest in radio spread, many manufacturers started making sets available, including those made for the new RCA company by GE and Westinghouse, and the precursor of Zenith, Chicago Radio Labs. Just a few examples are shown here:
http://www.sparkmuseum.com/REGOTH.HTM
So you see it's not really possible to say who was "the first." You could say that Edison made the first successful light bulb in the United States, or the first successful phonograph. But there were many variants of radio available as it grew. I have an Atwater Kent Model 30 from the mid 1920's, and an RCA Radiola III from 1924. Would like to have some earlier ones: I really like the sets from the earliest wireless era, love the history connected to them. We are getting close to when they would be 100 years old!