Pros: I like to record important phone calls, such as those to insurance agents, customer service reps, and telemarketers.
I used to hold a mic up to the earpiece and another up to the mouthpiece of my phone.
Now I just plug my recorder into this box and hit record. It works fine.

Cons: It's incredibly quiet. You have to crank your record volume.
I have a battery-powered recorder. I read here that if you try to plug into something like a computer, on main power, you'll get terrible noise.
I haven't tried this.
The jacks weren't labelled on my device. They were reverse of the images I saw on DX. You just have to figure it out by trying.

Other Thoughts:

Bottomline: It's quiet, but not especially noisy on my recorder. It's mono. I have mine permanently connected to my phone line, sitting on top of my computer with an audio cable always attached. I can plug in my recorder whenever I want to record something.

Pros: For this price, it can't get any better. It's very simple and effective. Just plug the phone cables, and another one into the computer's mic. That's it. Any software (like Audacity, which is open source) can record you conversations in a snap! Inner circuit eliminates noise and interference, providing good quality into the computer mic.

Cons: Remember to use a mono cable extending from the base into the computer. Stereo cables will generate a lot of noise and interference.

Other Thoughts: I live in Brazil and consumers face a horrible reality of product/service support via telephone. Companies will do everything to passively ignore your consumer rights and recordings of phone conversations are constantly (and conveniently) lost due to technical problems. This product is ideal to record consumer support conversations for later use in small claims court.

Bottomline: Great buy! You can find all sorts of equipments that do the same thing for hundreds of dollars more. Certainly worth it for this price. Anyone with average computer understanding can setup a recording station using freeware found on the net.