If you're already using the Nautilus, you're probably already doing direct lung hits, since the Nautilus doesn't really work well with Mouth to Lung. That being said, I just recently made the same move, and it was a real game changer for me. I started off with a Vapor Shark rDNA 40, and it's a great mod, but when I stepped up to the Sigelei 150, my world changed again. I found that I really, really liked a warmer vape than I thought I would, and the flavor and vapor produced by the RDA's are amazing. Depending upon the build and the juice, I now run the DNA at full 40w most of the time, and my Segelei anywhere from 60 to 80 watts. I also still run my Atlantis and Kanger Sub-Tank on either mod (great for driving), but I have to turn the watts down for those.
After a month, I've now got 7 RDA's, and my favorites are the Wotofo Troll, the Mutation X v3, and a Polished Tugboat. I like a deep juice well to reduce the incidences of dripping, and a lot of adjustable airflow. Vaping has now become a very intense hobby for me, and I love trying different coil builds and experimenting. Go for it! I think you'll love it...