These horns have a very interesting key mechanism: only two RH palm keys that do the work of three. In actuality, while the altissimo E/F vent key is eliminated, the function is not. What essentially happens is when you play high enough (high B and above, if I remember correctly), a double spring "activates" the chromatic side C key as the altissimo E/F vent key. This sounds like a kinda freaky idea, but this same feature was found on the late King Voll True and early Voll True II -- which was produced at about the same time (and for about as long :)

I've recently acquired one of these horns, s/n 103xxx  (which is why this model is now on this 'site :), and I really like the look and feel of this horn: it's EXTREMELY heavy -- probably the heaviest Martin alto I've ever played with -- and has rugged construction, has somewhat less radically bevelled tone holes than the Handcraft and a lighter feel to the keywork.

Please note that the baritones pictured here are in the correct serial number range for this model, but have the standard Handcraft keywork.  It was a common practice for baritone and soprano saxophones to be a model behind -- until demand got high enough for the new model to be produced. In this case, they are two models behind.

Also note that these models may have been available in bare brass, rather than lacquer. It is generally accepted that lacquer was introduced around 1934.