I've tried both in my system recently as they are cheap tweaks!
The HiFi Tuning fuse improved the high and low frequencies and seemed to open up the soundstage further in my system, so overall a definite improvement.
Isoclean certainly improved the treble in my system, more so than the HiFi Tuning fuse, but did little with the bass and the soundstage seemed to shrink, compared to the HiFi tuning fuse.
I now use 2 HiFi Tuning fuses in my main system and use the Isoclean fuse on my AV system as these audiophile fuses do improve picture quality on my TV. I think for the improvements in MY system, they are well worth the money!