[Edit Oct 2022 after owning 18 months: After charging the unit yesterday, I discovered that the little green square cover on the charging plate had been lost, leaving a glob of glue, exposing the metal plate. Quick response from customer service: it will now leak and be ruined, and the one year warranty is gone. I was offered a discount on a new one. Disappointing, but I suppose 1 1/2 years in the water is an acceptable life for this fun device. I do not know if it is the amount of use or merely the age, but a glued-on part, whether merely left in storage or rubbing against my head and in water cannot be expected to last indefinitely. For now, I plan to either move the loose cosmetic tab from the other side over the charging plate (but what kind of glue to use?), or put a little piece of duct tape over it. That could give it an extended life, I suppose. Also, re my note below where I discussed the advice about cleaning the contacts, I never encountered any build-up on the contacts, so I did not need the calcium remover chemical; furthermore, given the apparent fragility of the glued-on part, I suspect exposing that to any unnecessary chemical attack may not be wise.] I have had my waterproof Finis Duo MP3 player for 5 months, swimming laps in pool 4x/week, and I like it. I have very little previous experience with other listening devices, but I wanted something for this purpose that would allow me to keep water out of my ears. The sound is fine for rock music, and my ability to decipher the words is no worse than a car radio, but it is way more enjoyable than counting strokes to myself. The sound bypasses the ear canal, eardrum and ossicles through bone conduction directly to the cochlea. I wear multi-use disposable silicone earplugs (CVS). Without them, the sound will not be as clear. Bluetooth apparently does not work through water, so you load the MP3 music files onto the unit’s memory directly from your computer, and can delete and/or add anytime (4GB of flash memory). I haven’t used iTunes for this, but one may need to convert iTunes music to MP3. The files I loaded onto my Duo were already MP3 files. I can only guess an MP3 book file would work, too, since I just read that those files are about 280MB for 10 hours; however, I don’t know what I would do if I missed an important sentence and had to go back. Finis company was very good at answering some questions I had via email. I got some tips from reading other reviews, too. You should charge the lithium-ion battery for 24 hours before first use—maybe it won’t hold a charge if you fail to do this the first time. You can charge on a fast charger on wall safely, but don’t store the Duo unit itself on the charger. Battery life claimed of up to 7 hours, though I cannot attest to that. I chart mine every 2 or 3 uses (half hour swims). It took me awhile to memorize the buttons and their use. I’m still unsure when the toggle at bottom is on random play or not, or whether that resets after turning the unit off. I also have another question for the company: Even though I turn it off before connecting to charging, why has it started playing recently when the charging finishes? I suggest looping just one of the 2 straps of your goggles to the unit if your goggles have an overlap in the front. I had to fiddle with this carefully for several weeks before deciding the best connection to avoid the device from lifting goggles off my eyes, while allowing the speakers to fit just in front of the ear over the zygoma, a.k.a. cheekbone. You may prefer to have yours on the insider strap loop, rather than the way I currently have mine (photo). Once I figured this out, I leave the unit attached to my goggles permanently to avoid breaking the clips. I noted a previous review suggested using CLR- calcium, lime and rust remover instead of alcohol, so I bought some, but have not needed it yet. Six hours at full strength as reviewer suggested may be excessive, because it took some of the finish off a faucet I tried it on. Bottle instructions say far less time and at half strength.