Mike, i understand that you want to get normal TTL exposure at fast serial shooting camera mode ("Continuos shooting mode"), maybe 3fps - 7fps or faster. You don't like 1-2 seconds interval for Z240 recharging for accurate TTL. i can understand it.
Did you try such fast serial shooting mode with Z240 TTL in the past? Because, using Z240 strobe in TTL mode, Independently of anything, every next shot in fast series has significantly less lighting than previous shot, - Z240 does not have enough time for recharging and it causes different pre-flash (and different main flash) at every next shot. The idea of TTL metering does not work normally for serial shooting with small uw strobes.
People usually shoot in "single shot" camera mode with Z240 TTL to get accurate TTL exposure. This is independently of camera brand and TTL-Converter brand.
But Ok, you can find any TTL-converter which has very short pre-flash (Nikon, or other), and get 2-3 shots by Z240 this way in series, but it will not be normal TTL exposure (very different flash exposure for all 3 shots).
Hi Pavel. After I returned home from my trip with the UW Technics TTL board, I did a comparison bench test, using both the Technics board and the onboard strobe taking rapid secession shots. I did not get the same results you describe above, the three shots I took with the onboard flash TTL all seemed to be exposed exactly the same. I made a video of this test to send to my dealer to help explain the trouble I was having. I can post the vids here if you like.