The Touch N Flow applicator (TnF) is unique in the field of modeling tools, as it allows the modeler to carry a significant amount of thin liquid cement to long joints in confined spaces, which is especially helpful in ship or large airplane modeling projects.
While simple in construction, using the TnF applicator requires a bit of technique, because if the applicator is tipped so the fine tube end is lower than the glass tube, cement will flow, the steeper the angle, the more cement will flow.
Once cement has been drawn into the tube, the technique required to keep it there is to transport it in a level attitude to the model, moving the applicator to the joint in a level attitude, then tilt it up to allow the cement to flow. Not keeping the tube level will allow plastic cement to drop onto the model's surface, possibly ruining surface detail. It takes a bit of practice, but keeping the cement in the tube and off the model is a skill that is easily learned.
In some instances, the tip may become clogged with plastic from a joint. TnF recommends setting the tip in liquid cement to dissolve the plastic. That usually works, but can take some time, and modelers have discovered that a high E guitar string can be inserted in the metal tube to clear the blockage, minimizing down time. I have two applicators so I can soak one, and have a spare if one breaks (the TnF uses a tempered glass tube that requires some caution and care when using and storing it)