Hey,
I'm not familiar with all products that are out there, but Repton is a general multivitamin. How good is it? I personally don't know.
For a panther that is only going to live inside with UVB and not going outside, I'd probably dust with a multivitamin 2 times a week and calcium with D3 twice a week (alternating). Once the cham is 6-8 months, I'd start slowing down to once a week of each. (I like herpavite as the multivitamin and Rep-cal calcium with D3, though that's just my personal preference. Other products are good as well, just do your research...)
If your cham is getting 45 minutes of sun (not through any glass) I'd probably do calcium with D3 maybe 1 time a month, but would supplement calcium powder without D3 2 times a week. (Remember, the sun will create it's own D3 and you don't want to deal with the cham getting too much calcium into the system) I'd still give vitamin 2 times a week until 6-8 months of age.
Do remember that most supplements don't have much of a shelf-life once opened (even though it is not on the label.) Every 6 months, I'd toss old supplement (and there is usually a lot) and get a new supply..
Good luck,
Matthew