I don't know how costly it is to have UL listed or any other certification, but during my search all 2.5A and 4A fuses have UL and SA certification, except of course for HiFi-Tuning fuses. For instance, the Isoclean fuses have UL SA PSE and CE certifications, the Littel Fuse fuses have UL, SA and CE certifications, and Buss fuses have UL and SA.
It seems to me that they pursue the certification in the market in which they will be distributed. I don't know the certification story of HiFi-Tuning, but if they have it, it is odd that they don't post it like everybody else.