The 2.1-channel design offers simulated surround via Sony's S-Force Pro Front Surround tech, and Dolby Digital decoding via both HDMI and optical. If you were expecting Dolby Atmos this isn't something I've ever seen for this amount of money.
The Bluetooth link with newer Sony TVs uses an automatic A2DP connection, but if you want to stream music via a phone, it seems you will need to turn the TV off first.
The drivers are rectangular -- for greater surface area, the company says -- and the driver surrounds feature a notched design which Sony claims reduces stress on the edge of the diaphragm (i.e. it controls distortion). Meanwhile, the wireless subwoofer features a 160mm (6.3-inch) driver.
In terms of competition there is no scarcity of excellent $300 soundbars, including the Klipsch Cinema 400 and the Polk Signa S3. If you own a Bravia TV, the wireless "synergy" with the HT-S400 is something you can't get with another brand's bar, though companies like Samsung offer a similar feature.
The HT-S400 is priced at $300 and will be available in April 2022.