A UBCD4WIN is a must have for every windows user who changes hardware frequently, troubleshoots others pcs. It can be customized with many addons, but it is basically a Bart's PE with some useful modifications and addons. Hiren's CD is an UBCD4WIN except that he added software thats not licensed for general distribution such as Ghost and True Image, i.e. not freeware, and there is nothing in it that cannot be done with other software that is legal either freeware or opensource ( I know that opensource is not always freeware). Thats why you may have trouble finding a trustworthy source for its iso.
That said, Knoppix Live CD was and is an awesome (innovative) idea - and it never ceases to amaze me with what it can do. I have put it in ancient pcs and it booted right up without a problem, found appropriate drivers even for obsolete video cards and presented a nice clean display, connected to the internet without a hitch, recovered files off windows drives. After using it for the first time, it opened my eyes to world of Linux that I had never been interested in before.
And the surprising part is that the creators of Bart's PE, Knoppix, UBCD4Win are doing this primarily as voluntary projects with no expectation of significant monetary gain.