I've tried it in my chunk gun. It improves groups noticeably, but it requires good consistent wiping between shots, at least two patches, wet then dry. The thicker the base material the better mostly. I can get close with thick non Teflon material, but it also requires wiping for best accuracy and I need to be really careful with the wetness of the patch, too little or too much lube causes fliers.
Long term, I'm undecided. The Teflon is easier to use when last bit of accuracy can be taken advantage of, but it requires extra step between shots and I worry about long term buildup without some sort of strong solvent during cleaning. When I convert my chunk gun to .50 cal., I will reevaluate. I think many if not most chunk shooters use Teflon, but it is not allowed in strict table matches and I've seen and read about some good strings without it.