'Lovejoy type' is a bit vague as they make several types of couplings, I prefer the Uniflex type, they have zero backlash, high load capability and will tolerate a high degree of mis-alignment. The Sflex type have a much higher inertia and also have a degree of backlash.
Helical are fine for encoder coupling, if you use this type for motor/load coupling, you should use Stainless not aluminum. They are fairly expensive in stainless.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.