A very good sub for my listening preferences, rich in bass both in 5.1 movies and in electronic music that I listen to. Excellent build quality from a company with a name in the audio field.

Nice subwoofer with full sound. Definitely better than a Jamo 150W that I had (which was downfiring and quite boomy/muddy).

It requires attention when matching with the other speakers, it needs to have a relatively low gain in order to calibrate properly (I tried through Denon Audyssey, where it lowered it to almost -12db at around 40% and I had to manually lower it even more).

I replaced a Yamaha SW-P30 6.5inch 50w in a 2.1 Pioneer vsx 820k amp and JBL Control 5 speakers in a 35sqm room.
I had to adjust the amp's output for the SW to -10 db so that the gain knob reaches about 50% and the sub performs correctly. At 0db, the gain was acceptable at around 1/4 or maybe even less, and the performance was not good.
With the xover set at 80hz from the amp, I also had to adjust the Crossover switch on the sub to around 80-100hz, although it is recommended to be at max when the output comes from LFE. It is mentioned on the Net that reducing the xover on the sub smooths out the frequency response.
After these adjustments, the sub performs better in music mainly, which is what I'm interested in, but also in movie effects and games that I tried. I can't compare it to anything other than the Yamaha I had. That one barely covered the Control5 in terms of volume. The Klipch has a lot of power.
Since I also bought a special sub cable, I don't think it helped anywhere compared to a simple RCA cable, at least with a length of 3m.

Simply excellent, which perfectly matches the rest of the Klipsch reference series speakers. If there is space with a few extra euros, it is worth getting the 12-inch for even higher volumes. As Klipsch says in its motto "say hello to your neighbor" with the clean, full intensity of the music that the speakers produce.

***Edit after about 8 months since the purchase.
Personally, I bought it from a store in Germany and it cost me 268 euros including shipping. The speaker is excellent and matches perfectly with the Klipsch RF35. The 12-inch was about 40 euros more, but my space is limited. I enjoy them every day at volumes ranging from ~0db to +10db, and the neighbors simply enjoy quality music for free!!! You should also purchase a good quality RCA cable to avoid interference, as I experienced with a cheap cable from eBay. The Inakustik Cable RCA worked perfectly in my case, despite the 10 meters distance from the amplifier.