Bob Faster (@bfast) did a fantastic job testing flasher units suitable for LEDs in our E-Types in this thread: LED Flasher comparison
Unfortunately, it just seems that there are a lot of variables to this issue, and it is still a bit hit and miss. Since the flasher units need to sense the load from the indicator lamps to operate, it seems that you need to pick a unit that matches the precise LEDs you are using. Based on Bob Kirk’s experience, I am now concerned that though the CEC flasher unit is currently working with my Superbright 28 LEDs, it may not continue to do so reliably. I may have to pack the original flasher unit and incandescent bulbs in my road trip spares, which I’d hoped to avoid…