My car is eight years old and it has a very adequate sound system -- one that was pretty nice in its day -- but it is not MP3 friendly. The CD player won't play MP3 encoded disks. It has no USB input port, and no auxiliary inputs for an external MP3 player. I do have a cassette player in my car. and a cassette adapter is an option, but then I have to figure out how to keep my MP3 player charged on long trips. This is starting to get into a lot of wires to fumble with in my car.
Enter the Soundfly. In principle the Satechi Soundfly MP3 player and FM Transmitter is everything I should need in order to add all the missing features to my car's sound system. It is a small device that plugs into your cigarette adapter. It has a built-in MP3 player that works through the FM radio in your car. It will play music or audio books from a USB thumb drive or from an SD memory card. It also has a standard jack for an input that it will also transmit to your FM radio so you can use it with an external MP3 player, or a computer, or your phone, or whatever.
One theoretically handy feature is that when you are using its built-in MP3 player it will remember which track you were on and resume at that point when you power it back up after a stop. What should be even better if you listen to audio books is the ability to set a bookmark so it will restart at exactly the place in the chapter you were at when you stopped for gas. If you are thinking about buying the device as Satechi currently sells it you should know that the first feature--going back to the same track you were on--works great, but the second feature--setting a bookmark--is mostly useless due to a firmware bug that prevents its use past the first few minutes of a long chapter. More on the firmware bug later but first a few more impressions:
The FM modulator in the Soundfly is the best I have ever used. Most FM transmitters for your car hiss and buzz and fail to block out competing external signals which, for some reason, always seem to be the sort of obnoxious hip-hop which is most unwelcome in the middle of you Jane Austin audio book. But with the Soundfly I simply own 88.5 on the FM dial as my personal private frequency.
If your radio is compatible with the radio data standards the Soundfly will display the MP3 tag information on your radio's information display. My radio is not compatible so I can't speak to this feature. All I have to navigate with is the three-digit display on the unit itself which briefly shows the directory number and track number on your memory card or thumb drive when you enter a navigation command and usually shows the FM frequency.
The unit itself has a few control buttons but many of the buttons you will need for audiobooks--fast-forward, fast-reverse, next and previous track and folder--are all on the small remote control. In general I think remote controls for use in your car are silly but this one works ok and there is, I guess, something to be said for a hand held device where you can use muscle memory to find the buttons instead of taking your eyes off the road to look at something plugged into your cigarette lighter socket.
As to the firmware bug I mentioned it happens when the unit is performing operations that require a timestamp in the file it is playing. My guess is that the variable or register they are using will not hold enough bits to save a timestamp past, say, the fifteen minute mark in a track. If you have a single track that plays longer than fifteen minutes the Soundfly will play it fine as long as it is not interrupted but if you try to save a bookmark past the fifteen minute mark it will fail to save it, and if you try to fast forward past the fifteen minute mark it will jump backwards to somewhere near the start of the track. This means that if you have a thirty minute chapter and a twenty-five minute commute you will arrive at work with five minutes of chapter left to play and, unless you sit in your car and listen to the end of the track before you report for work you will spend most of your ride home trying to get back to the point where you left off.
There are several books where I simply never heard the end of a few chapters and others that I only heard because I listened to them on my computer after I had arrived home. It is a maddening process. Your objective is to fast-forward to minute fourteen -- just before the unit will get lost -- and then repeat eleven minutes you have already heard to get to the part where you wanted to set a bookmark but couldn't. The problem is exacerbated by the fact that there is no way to know when you have reached minute fourteen and if you go too far it will skip back to near the start of the chapter and you have to start over.
So, the bottom line is that if you want it for music (where a track seldom runs over fifteen minutes) you are golden. Buy the Soundfly SD, you will love it. If, on the other hand, you are looking for something for audio books and/or podcasts then you shouldn't consider the Soundfly until such time as they fix the firmware. I had mine for three months, during which time the long-suffering Satechi customer support guys were promising me a replacement with corrected firmware "Real Soon Now" but they finally said they were struggling with the firmware upgrade and wanted to refund my money. Since I really like their FM transmitter I requested, instead, that they replace the unit with a similar one they offer that is designed to work with Sandisk Sansa MP3 players. I have a Sansa E250 that it should work with. Hopefully, with my E250 and a Satachi FM tranmitter and car charger I should be good to go. But I still plan to pester Satechi tech support about the Soundfly firmware upgrade. It was supposed to be exactly what I wanted. It was a near miss. I'll buy another one if they ever make one that works.