I got my copper bottom cup about a year and a half ago for a recital and it really is as good as everyone is saying.
The great:
-Every note speaks and responds well, no more rolled up 3x5 cards stuffed in the opening. Loud, soft, high, low, legato, hard accents, it just works.
-Pitch and articulation clarity are consistent and reliable.
-It projects and doesn't cut the volume down nearly as much as other cup mutes, so you can play softer, use less effort, and make longer phrases compared to other cup mutes
-It's much more travel friendly and space efficient. I don't know if the cup portion will ever permanently deform, but it's been good to me so far.
-I love the sound on the copper bottom one.
-You can move the corks up and down so the mute is further in or out of the bell. I have mine about 1/2 and inch lower due to my conn bell taper pushing the mute a little further out of the bell.
2 1/2 things to consider:
-While I don't think it's actually any heavier than my Jo Ral cup mute, it feels a little bit heaver, or at least that the center of mass is a bit further outside the bell. It's only noticeable when using it for long stretches of continuous music, though.
-I have a Conn taper bell (which has a narrower throat where the mute sits) and so it seems like it sits further out because of the shape of the mute or the cork thickness/placement. I say this as I have to really push the cup up to get a seal on my bell to get that more covered sound. That undoubtedly contributes to the feeling of being slightly heavier. The adjustable corks help alleviate this problem.
-The corks can shift a bit when rotating the mute to put it in/take it out. It never caused an issue for me, but it might over time. I fixed this by putting the corks a fraction of an inch in the opposite direction I twist the mute when I insert it so it lined up when in the bell. It felt very secure this way.
I'll probably never touch another cup mute again after this one. Highly recommended.