Pros - very flat frequency response, wide soundstage (for earbuds) good definition and separation.
Cons - cheaply built, easy to fake.
Looking at the picture of the PK3's I wasn't expecting much. They look and feel cheap using a generic case for the drivers making them easy to fake. (In fact my first pair were fake!) these earbuds sound GREAT! Especially considering the price ($44) I have a few pair of earbuds in this same and higher price range and these PK3's knock all of them out of the water. They have a flat sounding frequency response some say a little bass heavy but i don't agree. What surprised me the most was the large open soundstage not common in ear buds. Using sansa clip + with rockbox.
The PK3 is a great, warm earbud. It does vocals especially well because it is very mid-focused. It has impressive bass extension, not especially strong impact; the trebles are smooth and may roll off too soon for clarity and detail nuts. But the mids are what the PK3 are all about.
Pros - Price, full-sound, comfort of form factor...
Cons - Not isolating, need to burn in before you judge...
I bought both the PK1 and the PK3 because I wanted to see what the difference was. The PK1's sounded better at first and I didn't want to spend too much time using the PK3 if I was going to sell them to a friend at work. BUT...that friend bought them and burned them in. They now sound GREAT at $40. Other people who sit next to him now want them. I decided to keep the PK1 and will buy them an amp which they need according to EVERYONE to drive properly. My recommendation, though, from earbuds you got from your player is to buy these and live with them for a while. Enjoy them and then see if you need more. I've tasted other good headphones and so I wanted the cleaner PK1's and will buy an amp to drive them properly. (An amp is needed if the headphones need more voltage or more current to be able to handle swings in voltage or enough voltage to drive inefficient headphones. It is not just about volume but about enough capacity to deliver clean and sufficient power for complex input/output.)
BTW, design gets good marks because they feel good in the hand and they don't draw attention.
I may buy the PK3 again...and love them for working out and grabbing them on the go without an amp.