Rod choice really depends on hair length and thickness, not just avoiding a poodle look. For shorter men's hair, smaller rods can actually provide better curl definition.
Larger rods work best for most men's hair to avoid a poodle look. Always check for previous color treatments before applying the solution. A quick texturizing spray can help them style it at home without much fuss.
You mentioned checking for previous color treatments... what specific things should we look for that would change how the solution is applied? Like if someone had box dye a year ago versus a salon bleach more recently.