I admit it - I'm a sucker for new devices.
So when I saw that the local dollar store had a bunch of these transmitters, I purchased one to try out. I've had some good luck in the past - a little while ago I got a Maxell FMT-1 off e-bay for $1, and it worked surprising well, both in terms of range and sound quality.
The first thing I noticed after opening the package is that this little device is both FCC Part 15 and Industry Canada RSS210 approved. Good thing, since it was purchased in Canada.
The transmitter consists of a cigarette lighter plug to provide power to both the transmitter, and a USB charging outlet on the end of that plug (so you can charge your phone or power other devices that require 5 volts). That plug is connected to a small, rectangular-shaped transmitting device with about 12 inches of cable. The transmitter is frequency agile, with a digital display, and has the ability to transmit (switchable) in either mono or stereo. Frequencies can be set manually, or you can use an autoscan feature to find an empty one (I found the latter a bit problematic in the crowded FM band). It also has an undocumented feature that lets you to change it into EU mode and transmit outside Part 15/RSS210 frequencies - that, of course, voids the certification and can get you into trouble from regulatory authorities. Finally, input to the transmitter is provided by another approximately 12 inches of cable, with a 3/8 inch stereo plug end (old school, no bluetooth).
Build quality seems OK, but in reading reviews, apparently the cable connections to the transmitter circuit board can fail after use (and possible abuse), as they are directly soldered on. It might be wise to provide some sort of cable support if you were going to toss this around in your car.
Sound quality and range, from my few tests so far, are about what you would expect from a car device. Find an empty frequency and it's good - it certainly fills your car, and I'm sure would fill a room. I haven't tested the range outside the confines of my car (that's next). I plan on using the device as supplied, and then, because the antenna is likely the audio cable connection, seeing what would happen when I use an extension cable. I doubt, based on what I've seen (and heard) so far, that this will take me outside low power compliance in either the U.S. or Canada (certainly not in Canada).
So, if you have a couple of dollars lying around, and you're lucky enough to find one of these, I'd do so before they disappear. I plan on using it to play cassettes through my car radio when the mood hits me (I still have lots of music in that audio format only).
I liked this thing so much I went out and bought a couple more to use as spares. Heck, for the price I paid it can cost much more to find a quality car USB charger alone.
