Actually, the tube connectors are not that great. You still have two solder connections and a connector.....it may have a shorter connection than most connectors but not as pure as a WBT Nextgen with low mass pure copper connections. My plastic clamp system is the purest sounding of all...and you can clamp wires together without any connectors.....less is more, most of the time.
The main problem with the tube connector is just what you stated: you have to use a banana into it and you cannot jumper to another connector or add more goodies like Music Purifiers. What if you have an expensive speaker cable with spades on it?.......then you cannot use your cables without a terrible signal distorting adapter. Using cables with no connectors and clamping together sounds like a hard solder....the purest sound. Here are three pics (bottom of page) of my plastic connectors (which cannot take bananas):
http://tweakaudio.com/EVS-2/Digital_amp_mods.html
You can also see my plastic clamp system on the xover for the Apogee speakers in the last link......two posts above. He loves them. He uses the Fidelium bi-wire adapter and has Music Purifiers and Ground Enhancers on each set pf posts for best sound.......so, is clamping the Fidelium cables directly to the wire going into the xover. His speakers sound amazing!