I'm using tube connectors on my GR-Research speakers. I've also used them on a few of my DIY amplifiers in addition to traditional binding posts.
I can't say that I've heard any significant improvement comparing tube connectors to high quality binding posts, but I also don't think they are any worse, and are certainly an improvement over cheap binding posts. They are also considerably less expensive than high quality binding posts.
The disadvantage of the tube connectors is that you are giving up some flexibility. The female connectors work ok with banana plugs, but obviously can't accept spades. Another disadvantage is that they don't hold as tightly as spades or locking bananas, so if your speaker cables get jostled at all, the chances of them getting disconnected is much higher.
I have some speaker cables with the male tube connectors, and in this case, I could definitely hear a bit more detail and image focus with the cables plugged into the female tube connectors compared to plugging them into the binding posts, but I think the compatibility here is not optimal.
I have not tried comparing the exact same speaker cable with male/female tube connector connections vs high-quality spades and binding posts, but my guess is that the difference would be minimal. Others have reported a noticeable improvement using the tube connectors (Ron from New Record Day, several members on Audio Circle), but I don't know the quality of the connectors they are comparing to.
So my (current) conclusion here is that these connectors provide a high quality connection (as good as a high quality binding post) for a significantly lower cost, but you give up some flexibility. If you've already got good quality binding posts on your speakers, I wouldn't recommend changing them.
Regarding the value of Danny's kits, I think @oldhvymec summed it up well. I will add that I've been very impressed with the NX-Otica speakers I built from Danny's kit and I believe he delivers excellent value in his products in general. He also provides a great deal of free support to the DIY community, so I try to reciprocate by purchasing from GR-Research when I can.
And as @oldhvymec said, the No-Rez is a well designed, easy to use dampening product. There are cheaper ways to accomplish this, but this is a pretty foolproof product that provides excellent results.
I can't say that I've heard any significant improvement comparing tube connectors to high quality binding posts, but I also don't think they are any worse, and are certainly an improvement over cheap binding posts. They are also considerably less expensive than high quality binding posts.
The disadvantage of the tube connectors is that you are giving up some flexibility. The female connectors work ok with banana plugs, but obviously can't accept spades. Another disadvantage is that they don't hold as tightly as spades or locking bananas, so if your speaker cables get jostled at all, the chances of them getting disconnected is much higher.
I have some speaker cables with the male tube connectors, and in this case, I could definitely hear a bit more detail and image focus with the cables plugged into the female tube connectors compared to plugging them into the binding posts, but I think the compatibility here is not optimal.
I have not tried comparing the exact same speaker cable with male/female tube connector connections vs high-quality spades and binding posts, but my guess is that the difference would be minimal. Others have reported a noticeable improvement using the tube connectors (Ron from New Record Day, several members on Audio Circle), but I don't know the quality of the connectors they are comparing to.
So my (current) conclusion here is that these connectors provide a high quality connection (as good as a high quality binding post) for a significantly lower cost, but you give up some flexibility. If you've already got good quality binding posts on your speakers, I wouldn't recommend changing them.
Regarding the value of Danny's kits, I think @oldhvymec summed it up well. I will add that I've been very impressed with the NX-Otica speakers I built from Danny's kit and I believe he delivers excellent value in his products in general. He also provides a great deal of free support to the DIY community, so I try to reciprocate by purchasing from GR-Research when I can.
And as @oldhvymec said, the No-Rez is a well designed, easy to use dampening product. There are cheaper ways to accomplish this, but this is a pretty foolproof product that provides excellent results.