There are many good and bad things about these headphones. I bought them for a friend of mine who was thinking a lot between DT-250 and DT-770. So, I will compare these two headphones a bit.
At first sight, DT-250 looked to me like a toy; they look very cheap and plastic and the visual appearance does not really suggest anything serious about this product. For example, DT-770, even though cheaper, looks like a high-end product compared to these. However, despite the plastic build and a cheap look, it seems to be much harder to damage or break DT-250 than DT-770. Another plus is that unlike DT-770, DT-250 have a detachable cable.
DT-250 are comfortable but they do heat the ears. The ear cups are not large enough and ears cannot properly breathe. DT-770 have much larger ear cups, which makes them much more comfortable than DT-250. On the other hand, DT-250 are smaller headphones and they are much more practical if you need to carry them around in your bag.
Unlike DT-770, the sound of DT-250 is going more towards something neutral with a good bass extension that goes pretty deep. Bass is elevated and might be too strong for some people or certain types of music. Due to the closed-back design and small ear cups, the sound is a bit boxy. Channel matching is not very good.
If you are on the move and you need something kind of neutral but sturdy, which will not break too easily then DT-250 might be a good choice. If you want a bit larger soundstage, more comfort and some sparkle then DT-770 would be a much better choice for a more realistic price.