Yeah, I've seen that before too. I've never tried it. If you can get your tortoise to eat it, fine. Or maybe you could grate it with a cheese grater over the food a couple times a week.
It actually smells really good I think that's what my tortoises like about it . I have seen my red foots and Russians eat it more than 3 or four times I just leave it in the enclosure and I let them do what they want .
My leopard and emys emys eat "moistened" Zoomed calcium block like its a main course. I often take it away from them.
With the block dry they still show interest though more controlled.
The block is made of calcium sulfate not calcium carbonate. From what I have read it should not have any negative impact on the system, I certainly haven't observed any in either animals in past 12 months.