Holy geez this thing is loud! Wear earplugs when you blow hard.
I had more luck using it in the print orientation (flat side down) than with the letters upwards. Maybe something to do with mouth airflow and bridging across the roof? I wonder if the problems people have with this are due to bridging at layer 91 which they cannot see due to it being inside.
I had a little bridge failure in the mouthpiece and had to trim a little hanger off. A manual support from 0mm to 4mm into the mouthpiece would help, but only S3D can do manual supports. Leaving a layer-height gap to the roof and wall-width gap to the walls is probably a good idea so the support can actually be removed.
Another option for letters could be to inset them just 0.01mm, which results in the slicer telling the nozzle to trace the letters in the first layer but still effectively making a flat surface.