I’ve not seen the new Weber cabinets, I was not that knocked out with the old ones. Other than old cabinets, I really like Weber products. I have seen the TAN kit and the cabinet, they both look good. You can see the TAN cabinet in my photos.
The Copper Cap rectifier is a solid state rectifier, which is basically 4 diodes, I think Weber puts a resistor in there too to provide “sag”. That would be a substantial cost saving over including a rectifier tube with the kit like you get with the TAN kit. Also, I think Andy is still supplying the extra power tubes with the TAN kit. If you like the idea of a SS rectifier (slightly more output, slightly more mids and tighter bottom end), you could easily build a switchable SS/Tube rectifier as I did with my 2nd 2Stroke. There is a drawing of the circuit in my 2Stroke photo album and you can see how I included it on the component board too. 4 diodes cost under $1.00.
An even easier way to add it would be to use the 4 unused lugs on the rectifier tube socket, then you only have to add a switch somewhere to select which rectifier you want to use. With a NOS rectifier tube you’ll get a browner, bluesy tone with sag.