Although it's a cool little toy and I'm glad someone made it, just to further the spread of such devices that play mp3s, there are a few problems logistically with such a device and most mp3 players short of ones that have a mini hard drive in them.
The fidelity will probably be too low through a cassette player for myself, especially if a lot of the mp3s you have are classical - I like to listen to classical sometimes when I work. Also, cassette players can skip and occasionally just mess up because they have moving parts. Thirdly, it's WAY too expensive, but then again most things are when they just come out, and it doesn't have enough memory. That goes for most players these days as well. Lastly, who even has a portable cassette player that works anymore (I know no one in my family doesn't anymore and we are kind of obsolete as a rule), and why would you put one in your car if you can make an mp3 player from scratch, with Linux as the OS, full ID3 support, a few gigs of space, and an LCD display for less money?
The only way that mp3 players are truly considered part of the regular music playing device category is when they are in everything - cassettes, high and mid-priced component systems, bookshelf systems, and when it's really easy to pipe music to them and there's more than 256 megs of memory (a gig will make it great, but an IBM MicroDrive will do). Removable media that could store that much would be great as well.
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