I recently purchased a Decade CM-10 (now discontinued) from a Canadian reseller on e-bay - it was supposedly a demo model.
I had issues right from the get go on the audio and range. Audio was very low, warbly and range was bad (barely a few feet). After some trouble shooting, it turns out that the ground isolator, which works on every other transmitter I have, was causing problems. Once removed from the audio chain, things started working properly.
Even though theoretically this transmitter should be tuned to Canadian BETS limits, range is still poor compared to other transmitters I own, such as the MS-100. I suspect that this is a Part 15 tuned unit, as its range is on par with the Maxell P-13 I recently purchased and did a quick review on (to be fair, range is a bit better, but the Maxell is intended as an ipod type transmitter, not a serious broadcasting device).
You generally get what you pay for, and this transmitter's cheap Chinese origins are apparent in the audio quality. Although admittedly subjective, it's not nearly as 'full' and nice sounding as the Decade MS-100 or my Landmark FM-350 (about on a par with the Maxell). Bass is lacking, and it sounds somewhat tinny at high frequencies.
I can't drive the modulation nearly as high as I can on the MS-100 or Landmark either - here, it's also comparable to the Maxell.
I've contacted Decade to see if there's a way to determine the country of tuning. I've also asked if there's a way to transmit in mono only. I'll post the results when I receive them.
Interestingly enough, even with its relatively short antenna (not tuned, at least in terms of length), I find that the transmitter's range is substantially more at lower frequencies - I obtained the maximum (several hundred feet before fence boarding on my car radio began) at 88.3, and it went steadily down as the frequency went up (just over 100 feet before fenceboarding at the high end of the band on 103.9).
Other than frequency agility and the potential ability to tune to Canadian standards, there really was little to recommend this device over the Maxell P-13. And the Maxell cost me US$1 (plus shipping).
Unless you can find one of these really cheap on the used market, I wouldn't recommend shelling out the money. There are much better alternatives available at the same or greater cost (US$100+), and much cheaper ones that give you equivalent quality.
And I wouldn't touch the untweaked Chinese transmitters readily available, based on this experience.