The GMP 450 is the closed back cousin of the GMP 400, which has an open back design.
 
The sound is very similar to the open back GMP 400, but with a little more bass response and narrower soundstage.  Very impressive though for a closed back design.
 
Interestingly, I found that the GMP 450 requires a decent quality headphone amp (I had them hooked up to an Icon Audio HP8) to really make them sing, whereas the GMP 400 was more flexible about it's source.
 
The earcups are mounted on what German Maestro call a cardomatic suspension system.  The result is a feather soft grip around the ears that readjusts as you move and stays pretty secure (as long as your not really active).  The cardomatic suspension is really rather clever.
 
Handbuilt in Germany and coming with a 3 year warranty, the GMP 450 from German Maestro is a very impressive closed back headphone.
 
Verdict:
 
A class leading closed back headphone that is equally at home in the studio or at home.  Nicely made, very comfortable and sound that is both refined and balanced.  Highly recommended.

The German Maestro GMP 8.35 D (and it's higher impedance relation the German Maestro GMP 8.300 D) are without doubt the toughest headphones I have come across.  German Maestro call them "nearly indistructable" and I agree!
 
Sound quality is very nicely balanced.  Bass response is rich, with accurate and precise trebles.  The GMP 8.35 D and 8.300D are both serious audio monitoring tools that are refined and insightful.
This is a reference quality headphone that is suitable for studio, home Hi-Fi or portable applications.  At a push you could hook up the relatively low impedance GMP 8.35 D to a portable audio player and take them out on the street. If you have a decent headphone amplifier then we would recommend the GMP 8.300 D.
 
The closed back design keeps you well isolated, ensuring a minimum of sound leakage in or out of the cups - as you would expect from a monitor headphone.  The ear cups fit comfortably and the headband keeps the headphones securely on your head.  As with all closed back designs you will need to vent the earcups every so often to keep your ears cool.
 
The GMP 8.35 D is sturdily made and will survive the the harshest environments (they look and feel military grade).  The headband is made from a band of steel and the earcups are made from a lightweight PE material that will withstand impact.
 
Verdict:
Built to a very high specification the 8.35 D and GMP 8.300 D will last forever and sound superb. Not everyone will like the no compromise, utilitarian design, but I rather like it!

The GMP 400 is handbuilt in Germany and comes with a 3 year warranty.  The GMP 400 is the open back cousin of the GMP 450, which has a closed back design.
 
The GMP 400's sound is very nicely balanced.  Enough warmth to make them an enjoyable listen, with an incisive precision that allows you to really hear all the hidden detail in a good quality recording.  I feel the balance is just right.
 
These headphones are like a mixture between all the things that are good about the Sennheiser HD650, the Grado SR325is and the Beyerdynamic DT880.  Not in your face like a Grado SR325is, not overly relaxed like a Sennheiser HD650, and not overly analytical like an AKG K701/K702.  More like somewhere between the Grado and Beyerdynamic sound signatures, which is a good thing!
 
The earcups are mounted on what German Maestro call a cardomatic suspension system.  This results in a feather soft grip around the ears that readjusts as you move, which stays surprisingly secure on the head.  A really innovative design.
 
Verdict:
 
Very well balanced sound, a high level of build quality and extremely comfortable fit make the GMP 400 a serious contender.  These headphones should definitely be added to the shortlist and demo'ed.