Fast-Blo ISOCLEAN fuse?

Just wondering, has anybody ever received a "fast-blo" type Isoclean fuse. This is where the fuse element is a thin wire with a solder-type bead in the middle, such as this picture:

http://www.allelectronics.com/mas_assets/cache/image/6/c/c/480x480-1740.Jpg

The last two Isoclean fuses I received (small 1A and 2A) both have this thin wire with a bead. I don’t know if they are counterfeit or not. The fuse had gold-plated end caps and proper Isoclean brand/arrow printing. It also came in a fully sealed Isoclean package (the cardboard mount with shrink wrap - also the instruction paper and the cloth cleaner, as well as the outer cardboard).  I have a couple other 1.6A Isoclean fuses that are the wire coiled around a non-conductive center pole, such as you can see in this picture:

http://www.phileweb.com/news/photo/200503/ISOCLEAN2_big.jpg

The fast-blo type Isoclean (with the solder-bead in the middle) sound bright in the high frequencies and they don’t have the fullness or body - sounds just don’t hit with the authority. The slo-blo types with the wire coiled around the center-pole sound much better. The highs are fast/quick and they are there, but they just sound right. It also has a lot more punch in the sound.

Anyone have any comments/thoughts on this? I’m assuming the Isocleans only come in slow-blo, as those are the only pictures I have seen and more than one retailer indicates that the Isocleans are all slo-blo.