LR on a twist is fine and not dangerous. It just might be a bit hot if one were to turn it up, though. That could burn out the atty quickly as well as scorch the juice.
LR was developed to simulate higher volt vaping (4.8 or 5 volts) on 3.7 volt devices. One does not need a LR on a vari -- as you can change the voltage. Also, as the twist is variable, it's not a low voltage device, imo. (to me low voltage are mostly mini ecigs). Before vari-volt and vari-watts we had fixed voltage devices only.
The key is to get the right voltage and atty/carto ohms combination to create the watts needed for your sweet spot -- or the sweet spot for that juice. It is often stated that most like 8-8.5 watts. Many like it hotter---even 12 and 14 watts--and I tend to like it cooler.
Just did a quick search and found this site that explains it all pretty well. It also has an ohms calculator.
Undestanding resistances, LR and HV
The beauty of vari -- is you can dial, use a screwdriver, push buttons or twist to taste. Atty resistances change as they age too--(often lower)--so having a vari helps one maintain consistency.