The Good: The compact Polk Omni S2 is one of the least-expensive Play-Fi multiroom speakers yet. It offers a big soundstage and lots of bass. The speaker sounds even better in stereo mode, and it's easy to set up -- unlike the comparable Yamaha. The Bad: No Bluetooth support. The Play-Fi app can be a little daunting for beginners. No way to adjust the sound quality -- no EQ, for example -- and it could sound confused with the wrong music. The superior Sonos One is only little more expensive. The Bottom Line: The Polk Omni S2 is a well-priced, versatile Play-Fi speaker with decent sound quality, but Sonos' shadow looms large. Sonos has been the best wireless multiroom audio system for so long, it's hard to remember a time that it wasn't around. And for the last 10 years at least, pretenders have tried to nab the crown for themselves. One of the most serious of these is DTS, the same company behind the theater and home surround-sound format. Its Play-Fi system has been with us since 2013 and is now supported by over 20 brands.I've reviewed several sound bars featuring Play-Fi over the years, but I haven't looked at a compatible budget speaker since the deplorable Phorus PS1. Unlike that wobbly first step into Wi-Fi speakers, the Polk Omni S2 is a polished product which offers fine sound quality for the money, and costs less than Sonos' superb entry-level One speaker. But unless you're already invested in Play-Fi, Sonos is worth the extra money.The Polk is a versatile little speaker. It can be placed horizontally or upright and offers a choice of either a black or a white cover in the box. And you'll want to use that cover because the bare drivers are pretty ugly, even by ugly speaker standards. At least you get four of them: dual 2-inch full-range drivers and twin passive bass radiators.The S2 measures 4 inches tall (or wide if you place it on its end), 9 inches long and 4 inches deep, and weighs 1.2 pounds (0.54 kg) . The version I reviewed doesn't come with a battery, but Polk does sell the $249 Polk Audio Omni S2 Rechargeable in case you want to hit the road.