My HD-300 is the only closed headphone that I have listened to in ages. Therefore, my review is certainly biased by my preference for open phones and my lack of experience with direct competitors.
All in all, this is a very good product, well built, comfortable and quite compact when folded. Insulation is good. The sound is very nice, slightly warm from my perception. Impedance and Sensitivity are appropriate to enjoy listening from the regular 3,5 mm jack of an iPhone or iPad. A dedicated headphone amp is not useful.
Still, the DH-300 pro suffers from the lack of soundstage and the sensation of having one's head in a box, that seam to characterize closed phones. I have read in some reviews of much pricier hifi-oriented closed phones that they don't suffer from these closed-can limitations. Given the 195 € price of the HD-300, which is not an entry level price, I had expected the HD-300 to sound more open. Maybe it was my mistake to expect this from a headphone designed for professional users and not audiophiles.
I can only compare the HD-300 to my Audio-Technica ATH-E70 IEM, that provide even better insulation from ambiant noise with the appropriate eartips and despite their own issues, the IEM sound much more open.
So 5 stars for all criteria, but only 4 for my satisfaction !