I've just received the following reply from Futaba support USA. So it looks like it's official although 'should be fine' is a bit vague

Hi, I've seen that manual as well. It's annoying that the manual for the SBD-2 gives a specific voltage range but the SBD-1 doesn't. I've actually raised a service ticket with Futaba in the states to try and get a definitive answer. It's good to hear from Gary that he's had no problems but I'd like ...

Thanks for that. Appreciate it.

That's good to hear. Can you tell me what servos you had attached to it? Were you using all 3 ports at the same time? This is going to be controlling the rudder and split elevators on my plane so obviously it's critical it's reliable.

Hi,

I'm planning on using an SBD-1 to control some Macgregor HV servos. Has anyone used the SBD-1 in a 2S lipo setup before? I can't find any mention of the actual voltage range of the SBD-1 in any of the manuals.

Thanks,
David