It's random eBay purchase time. I didn't get this to use mainly as an MP3 player, they're just getting cheap enough that when buying a portable flash device you might as well get one that can play any MP3 files you leave on the thing. So, without further ado...
As far as interface and supported formats go, it has no problem with variable bitrate MP3s (or ID3v2 tags) and files can be navigated by directory. Apparently WMA is supported, up to the recent version ten. I have no use for this, personally. Sound quality is good to these ears. No battery is required to use the drive via USB, whilst playback runs off one AAA battery. I suggest turning the backlight off if you find batteries are being drained fast, but I still have a batch of cheap AAAs (bought for a previous player) to work through that I don't expect much power from... ergo I haven't used Duracells or similar to test the maximum battery life. Eight hours are mentioned on the website, ten in the manual. The website is probably closer.
Transfer is facilitated by a female mini A-type USB connector, into which plugs a cable, indicating that this device is designed more to be used as an MP3 player than as a portable drive. I'm considering getting a 1½" socket adapter, as the cable is moderately cumbersome to carry around and most people I know have front-mounted USB sockets on their PCs. If you're thinking of doing similar, be warned that mini A-type male cables (4-pin) and adapters aren't common yet and only some USB travel kits come with them. Update: it's a hirose style connector, and adapters are much harder to find than cables.
There are two case holes for small cords, one for the supplied headphones to tie to and another for attachment to a lanyard. It's a bit annoying that the hole for the neck cord isn't on the bottom corner rather than the top, which would mean fewer entanglements with fingers when retrieving it to switch tracks. Naturally there's a 'hold' switch to prevent accidental adjustment. Navigation is provided by a switch on the side/top that can be rocked or pressed, plus a play/stop button and two more buttons for volume. By default playback resumes from the point you switched off at, so the player is suitable for listening to audiobooks and shows.
A nice extra feature (only for MP3, not WMA) is tempo control, which slows replay down without affecting pitch and makes picking out lyrics easier. There are also advanced segment replay tools, which seem both complicated and powerful; a voice recording microphone; the option to make some space on the drive encrypted; and the player will scroll lyrics if you have timed files for your songs. Most of of which isn't of practical use to me now and probably never will be, but I didn't know the full feature set when I bought this device and it's always nice to have options. Moving on to features I looked for but didn't find, although there's a 'Playlists' directory on the drive when mounted on a PC, I presume this has something to do with internal functions rather than being an indication that the player can read M3U and PLS playlists.
The supplied headphones are better-than-average freebies, but you may want to adjust the equaliser depending on what earpieces you decide on. A mini CD comes with the package carrying drivers for Windows 98... as ever, you aren't likely to get USB working under Windows 95 unless you have OSR-2, and even then it's unlikely to work.
Any gripes? Well, there is one small issue with playback of files inside a directory. The device plays tracks in the order they were copied to the directory, not based on filename or ID3 tag. If you just copy directories, Windows may not copy track one first because of the way it threads file operations. Basically, create a directory on the player, select the files to drag into it, and click-and-drag making sure that you began the drag by clicking on the first of your numbered files. That seems to consistently work. If you're making a playlist rather than copying a full album you could use the gen_yar plugin for Winamp, which copies files in order and numbers them.
All in all, it's a much better player than I expected for the price (£18 delivered) and the boxed preview image in the eBay auction. I would have preferred an integrated A-type USB connector and wouldn't be bothered if the device were chunkier to incorporate this, but overall I'm happy. A 128Mb player will currently set you back about £15 in-store these days, so this gets a boosted perceived value rating.
You may also be interested in the short list of portable software I carry on flash drives.