the website for one of these products says its basically just liquid vitamin D.
this might work well as a vit. d supplement (i haven't tried it) but i would hesitate to replace sunlight and/or UVB bulbs with liquid vitamins...
It's a concentrated vitamin D3. It looks like it could be useful in some situations, but caution is needed to avoid overdose. You have to know the specific species requirement. And no one knows exactly how much vitamin or mineral tortoises need..