At what point is it a good idea to switch from launch rods to rails?

I have a 4" diameter rocket that weighs
about 4lbs. It has 3/8" launchlugs that I haven't installed yet.

IMHO, rails are A Good Thing. I use rail buttons on a scratch 3" ~1.5 lb rocket & installed them on a 3" NCR/Estes Lance Beta. I plan to put rail buttons on anything 2" and up.

You also might consider installing both buttons and lugs. I did that on the above mentioned rocktets. You do pay a penalty with extra drag but get the benefit of expanded opportunities to snag a pad.

Friends in Texas recommended Delrin rail buttons as standard for their launches. Will those work with the rails available at our launches?