Hopefully this doesn't belong in another thread, but I just wanted to give my two cents on the MW 451 that I've been testing out for the past week and plan on purchasing.
My first impressions before I even played a single note were that the valves are very quiet (I have a habit of fiddling with the valves when I'm not playing the instrument), and that it is a very comfortable instrument to hold. Being slightly on the smaller side (5'7" 140lbs.) and with long arms, this will probably be a little different for most people. The moutpiece sits at the perfect height without the towel that I used under my Jupiter. Its a small issue, but is nice to not need to be messing with a towel/pillow every time I want to play. The reach to the fourth valve is perfect for me and it just seems to naturally fall into the right spot for me to play.
As far as intonation goes, I had to pull out the main tuning slide A LOT. However, the individual I took it to (who has been teaching euphonium for well over 20 years) attributes this to not being used to using a large bore instrument and that over time the pitch will center better as I get physically accustomed to the instrument. The sixth partial Eb is the only note that I could not bring into tune either with minimal lipping or manipulating a slide, and will have to use the fourth valve since it is just the slightest bit flat with the fourth valve.
It is very free blowing, and I love the color of the sound that is produced which is much richer and fuller than the Jupiter that I've used for the past 5 years.
I don't know if this means anything but I have been testing it using a Yamaha 51 mouthpiece, which seems to work well enough.