For value, they're probably one of the best headphones I can generally think of. They retail for around $300 CAD and out-perform many headphones for the price. I'd compare them to headphones of at least $100 to $200 more expensive. After an hour plus listening session against the HiFiMAN HE-400i, I still preferred the Custom Studio.
Detail is plentiful and full of energy. Very vibrant treble, lack of harshness or painful sibilance. Bass is full, well extended, and understandable; powerful. The mids are a little recessed. Still quite decent, but they don't have as much soul and presence as headphones higher up in price. Tonality is overall fairly balanced out - the V-shape isn't prominent by any means. Adjustable bass feature is nice, but unnecessary.
The soundstage is fairly wide and open, considering the closed-back design. Could do with a little more depth. Imaging, otherwise, is fairly easy to locate and interpret. Clarity is everywhere, but most detailed in higher frequencies; resolution exceeds the expectations for price point.
The build is tank-like. I've dropped them plenty, and nothing is wrong other than a few scratches. Easy to replace parts in event of worst case scenario. If I could change something it would be the clamping pressure. The velour pads are super comfy, but somewhat offset by how the band crushes your head. Should also mention that this particular set of cans gets hot easily in warmer weather. You might want to avoid taking this on long jogs.
Overall, this is a quality piece of hardware that performs extremely well for the dollar. The design is top-notch, and brings no concern of durability or design issues. Of the issues I can find, they aren't major. If the mids, soundstage depth, and resolution all improved a little bit - and I don't mean a great much - I'd be ranking up this headphone much closer to the level of K701/2 and HD 600/650 in performance.
Versatile, reliable - the Beyerdynamic Custom Studio is a king of quality, ace of value, and jack of all trades.
There's no gamble buying this one.