The ttl works fine, but the beam is narrow. It tends to get hot spots. I've been using it with the Sunpak on normal mode. They both fire and the ttl senses the second strobe. When I've had the strobes aimed well and not hidden behind kelp or a rock, I've had really good lighting with the FL-20 on ttl and the Sunpak on lowest setting. My lighting skills suck, though, so I've been hit or miss. Thankfully Raw Shooter and PS-7 cure a lot of photographic ills. I can usually save all but the worst black-outs and white-outs.