I'm not Manring but I don't think he has to use a tuner. When your doing alternate tunings you can use other notes on the neck as refrence points or strum cords and tune from there.
Although tuning by ear is sometimes nice, I usually use a tuner. I have several that I like including the Intellitouch. Usually on stage I use a Boss TU-12H. It's relatively fast and easy to see in all kinds of light (or lack thereof!).
Congratulations on starting to play fretless! It's a beautiful instrument and I think you'll get a lot out of it. In terms of advice -- be patient. Try to learn to enjoy the slow process of listening deeply and carefully building your abilities. Always look for ways to test your intonation and give yourself the opportunity to improve. And of course, have fun!
