I own every single Samsung U series in the market. Of course, it's not out of necessity that I own every U series. They are not expensive and I like the diverse design so it's a collection hobby. Seem like a unique hobby? But because of that, I also have all iPod shuffle. Of course, most of them are lower-end versions. I cannot afford to collect iPod touch! :)
The most recent series U6 is the most sophisticated out of all the products launched currently. It aptly combines the strengths of U4 and U5. I can see that Samsung has made a lot of efforts to incorporate consumer's complaints and improve the weaknesses. It has taken a bold move from the cute U3 design and is much simpler and sophisticated. The aluminum body similar to iPod certainly gives a more upscale look than plastic. For aluminum, there is the concern about the product becoming heated with long use, but for MP3 player, the device is so small that you don't have to worry about it like you do with notebooks.
U6 incorporates the strengths of previous products. First, the 'tactile quad-direction key' which was favorably received in U5, is applied. U3 and U4 had touch button, but those with thick fingers or those working out complained about the difficulty to manipulate. With the touch button, U4 had a much fancier design, but the weak touch recognition was a key cause of complaint. U5 incorporated these weakness and changed to 'tactile quad-direction key' button, which continued into U6.
Second, the USB has changed from a lid type to sliding type. U5 was a lid-type where you open and close the USB port connection. This ensured rigidity, but the risk of losing the lid was an issue. That is why U6 has sliding type like U4. And U6 is much more stable than U4. Unstable connection of U4 when connected to the PC is completely resolved in U6 that it connects firmly with the PC.
Third is the improvement in how the ear phone is plugged. I personally wanted this to change, and yeah - it's improved. I really want to thank Samsung for the improvement. For U5, the connection to the ear phone was next to the navigation button. So, when trying to control the button, the ear phone connection came in the way. It also created noise because I would touch the connection. But for U6, the earphone jack has been relocated to the opposite side. This was mentioned in some forums, and I guess Samsung proactively took measures.
As mentioned before, U6 is the most sophisticated out of all the series. I want to give thumbs up especially for improving the three shortcomings. I give applause to Samsung for listening to the consumers and incorporating them into their products. It would not be easy to compete at higher end because of the strong presence of iPod touch, but for lower end, I definitely think that U6 will be a hit!