A neck strap can make it easier to keep a controller close while preparing a shot. The mounting hardware matters just as much as the strap itself, especially when changing between controller models.
Check the attachment points
Lay out the clips, bracket and fasteners supplied with the strap. Compare them with the fitting instructions for your controller. Do not assume that a bracket pictured on an RC 2 will also fit a different controller.
Adjust it on the ground
Support the controller with your hands while checking that both clips close fully. Set the length so your thumbs reach the sticks comfortably without lifting your shoulders. Try the position with your normal jacket or camera bag on. Recheck the clips after changing the strap length.