I have seen him three times - first time opening for TGA in 2010 with the band and two times this past spring opening for the Dropkick Murhpys solo.
He is not my thing either but I have seen worse openers. Would definitely not ever buy tickets to his headlining shows. But he seems to have a loyal following. At the DKM show he brought a fan from England on stage who had apparently followed Frank opening for Social Distortion all through their U.S. tour. To each their own I guess. It's good not everybody likes the same bands.