A few weeks ago, I picked up a Polk AM1055-A sub (a.k.a. PSW10 / PSW108) to use in a small, two-channel set-up with a pair of ChaseHT WAF-3 speakers. I'd often wondered how a 50W, $99* sub would sound, and this was a good opportunity to find out.
(*It's frequently on sale at that price.)
Aesthetically, it's a nice little box with clean lines and a slick convex grille. It looks and feels well-built. It has line-level and speaker-level connection, and an "auto" power function. So far, so good.
I hooked it up to my Technics SA-500, ran wires to the WAF-3s and set the crossover to 120Hz. Then I played some music: Holly Cole, AC/DC, Jeff Healey, Iron Maiden and, just for fun, Bassotronics' "Sub Bass Excursion" (SBE).
At low to moderate volume levels, the sub performed pretty well. It played cleanly and provided a nice bit of thump when necessary. At slightly louder volumes, although it remained composed, it did start to get a bit boomy.
(The one exception to the above was when I played SBE: Even at moderate levels, the sub completely choked (severe cone flutter and port chuffing). I didn't dare turn the volume up any higher on that song.
Based on the hour or so that I did play with it, my conclusion is that this would be a decent sub for a very modest two-channel or home-office system in a smaller room. I don't think it would work very well in a large room (at louder volumes) or in any quasi-serious HT application.
YMMV, of course.