Well, I've had the thing for a few days, but I'm loath to make any conclusions...

*My practice basement isn't exactly an acoustic paradise. There's only a few feet
from the bell to the drop ceiling when I'm sitting, and the bell is right near the drop
ceiling when I stand.

*Since all my ensembles are on hiatus, I have no way to evaluate the cap as part of
a euphonium section or as a soloist. Additionally, all my ensembles rehearse in a more
reverberant space than my basement.

*Only my ears are listening. I've tried to solve this problem, but listening to me play seems
to produce a strong desire for social distancing.

*I do feel a bit of difference that I would describe as "more focused" or "more direct."
I tried it on all four valves--hard to tell if it produced any difference on 1, 2, or 3.

*I'm not feeling any issues with springs, though other reliable sources report issues.
Mike or Chrissie, could you please give us the email for this fellow Chris?

*I'm not sure, however, whether introducing a rubber spacing washer would reduce/defeat the intent of the cap.

*So I'm gonna keep it for now until I have a chance to play in a group with other euph players in a bigger space.
If it doesn't work for me, I'll sell it to someone for whom it may well work.

*As I mentioned earlier, buying a euphonium from a vendor is like buying a suit off the rack. Both may well need some
alteration to fit the owner better, though some owners are perfectly content with the suit/euph off the rack. I couldn't
leave a suit or a euphonium well enough alone.