Some Lamp tube talk here.
ECC40s were all made in the Herleen (spchk) factory cept for the Tunsgram ecc40s. I know from experience that the 5y3 or 6x5 rectis (depending upon which one you have) can be greatly improved with a NOS sub over the russian stock recti. Talking BIG improvment with a small ($10-$25) investment.
The Bendix is a interesting and rare recti sub but the circuit has to be modded to accept it. Without hearing it, I cannot comment. I'm suspect about it, since even NOS 5y3 or 6x5 is a huge uptick over the stock russian tubes.
I've read some people call the Bendix an aggressive sound. So between being stuck on having to buy a rare and pricey Bendix recti. NO tube rolling options, and doubtful I want my digital to sound aggressive, I will probably just stay curious unless, I get to hear it first.