The Bohrok Kal tend to be looked upon poorly, and that view is justified: They are indeed clone sets, they are indeed direct clones of the earlier Bohrok, and they are indeed fairly useless overall.
So why am I defending them?
Well, they did their job well.
The Bohrok Kal were, as far as I can gather, not really meant to sell like hotcakes, and were never intended to be the main villain of 2003 (obviously). What they were meant to do was fill the gap between the end of 2002 and the release of Mask of Light and related products - both from a story and set point of view.
Consider if the Kal had not been released, and MoL had been released in early 2003: We would have launched straight into a relatively Matoran-focused story, without spending any time getting to know how the Toa were handling their change into Toa Nuva. We would also not have had a good feel for how powerful the Toa Nuva were, and thus the Rahkshi may not have been as menacing, story-wise. The Kal arc showed us how strong the Toa now were, how they were interacting, and what was needed to defeat them (or nearly defeat them) now.
Just look at Comic 9, Divided we Fall - its first 8 pages serve only to show how powerful the Nuva are, and the remainder of that story arc showed us a.) What sort of threat could defeat them and b.) how they had grown as characters since their early days. It also served as an excuse to have the Nuva hunt down their Kanohi, so as to retain all their powers there.
Of course, this could have been done without the Kal - just have the opening 8 pages of Divided we Fall occur just before Takua finds the Avohkii - and I suspect that if Mask of Light had been ready for, say, February 2003, that's what would have happened. As it was, Lego needed a quick story to fill the gap, and sets to last five months or so. Given that Lego wasn't in great financial straights at the time (though they wasted money on those stupid Silver Krana), recoloured Bohrok were a good answer.
So, why do I say the Bohrok-Kal weren't so bad? Because they served the purpose they existed for, and gave us some nice recolours. Were they great? Hardly. Were they that bad? No.
But that's just my view - anyone agree?