Fortunately since I'm in South Florida my torts are outside everyday in natural sunlight so I do not need UVB lights. I do think this attempt to experiment with a new product has merit for indoor torts. Especially for those raised in open top tables under UVB and basking lamps.
Enclosed chambers with elevated humidity levels , soaking, water always available, have been shown over time to improve the desiccating effects of artificially light. This has been done by hobbyists experimenting with their own herds. Not a scientific based study - we won't get one of those. The $, times, & effort to set up a proper double blind study is not available. Our data is antidotal and we have to make broad assumptions of causal effects. But this is still good info and valid. Certainly convinced me to change my husbandry. And I'm a sceptic
Having said that, I see no real downside to measured shell application. The OP has shown a definite shell improvement in his own tort. I don't believe application to the skin is a good idea however.
The UVB lights D3 benefits are absorbed through the skin, not the shell. EVCO has a UVB blockage effect. I see no upside to putting it on their skin
Ahh waking up to your belief that this has some merit to indoor captive torts made my day. I was thinking about the fact that the majority of information on here was probably NOT the result of a controlled scientific study that came to these unbiased conclusions. Encompassing the entirety of basic and advanced husbandry. Observational data from both amateur and profession tortoise keepers seem to have a lot of pull if articulated correctly in this forum. I am seeing results from controlled application. Even if it's observational, the majority of information here seems to be observational in nature anyway.. I agree with the fact that the skin probably will not benefit much from application, unless it's a localized dry spot using a qtip. I think I'll stop applying it to the skin , except maybe the top of his wittle head seems to get dry easily. Otherwise. I have gained even more confidence in this debatable topic