I will say that the main advantage of the top sprung, short throw valves is the agility. I am approaching age 70 and have recovered from two broken fingers and three trigger fingers (two of which required surgery) on my right hand 1-2-3 fingers and thumb in just the last 5 years. Thus the light and short action of the valves makes it ideal for me. The light weight of my horn (yellow brass and no trigger) also makes it very comfortable.
In discussions with Miel Adams when I purchased the prototype, the major issue was cost. As a rough number, he threw out an incremental $1000(ish) over the cost of an E3 with the standard Bauerfeind valves. At that time, he had built up 5 sets of these valves, only one of which had made it into a saleable horn. However, these were not just one-off prototypes. Adams invested in the tooling required to make it a production item.
Another disadvantage (to a lesser extent) is a minor change in geometry of the horn overall. The length of the top sprung valves and position of the valve slides requires that the body of the horn be just slightly longer than a standard E3. This affects fitment into the Marcus Bonna case and requires a slight change in the length of the lead pipe vs. the length of the tuning slide loop (required removing 1.5 cm. from each of my tuning legs). All of this would mean it is not a straight plug into existing tooling, I would think.
I also agree with Dave Werden that the oval ports "might" affect the horn in some respect or other, however I have not been able to notice this. The prototype Dave played is (I think) the horn I currently own. It is a .70 yellow brass horn rather than the .60(?) sterling silver that Dave has. The only one that I know of that can comment on the impact of the short action valves on response/tone/intonation and any other playability is Mike Taylor, since at one time, he had two otherwise identical horns.
I hope this helps.
Doug
P.S. Mike, If I could somehow sell mine to buy yours, I would be very interested. But that is whimsical thinking rather than serious.
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band