Personally I'd keep them on Bml if they are already eating it and eating it well. It's an affordable consistent well known and widely used diet providing the recipe hasn't been modified.
Not to mention for new owners its probably the easiest diet to make when the recipe and feeding instructions are followed there is no guessing what to feed or what is safe.
The only time I consider changing diets is if and when my gliders stop eating what diet I have them on. But that's just me, there are more than one reason most people decide on a diet, cost, ease of preparation, online vs locally ingredients, storage space, ingredient preferences ie fresh vs powders etc...
But in the end the gliders always have the final say if they don't eat it the "best diet" on the planet won't do them any good.
There is nothing wrong with the repcal products in bml, bml has been tested with those 2 specific ingredients, changing those ingredients is changing the entire diet and likely going to cause an imbalance.
Not all calcium/multivitamin products are the same so if you change brands you could also be changing the amount per serving which then makes everything else in the diet imbalanced. Everything fed with bml factor into the over all balance of vitamins and minerals including the fruit n veg.
This is why its strongly recommended to follow the diet creators recipe exactly. If any changes or tweaks needs made to the recipe the creators will usually post the changes and why the changes were made on their websites.
Bml has not needed changed in sometime as far as nutrition goes. However one ingredient was changed last year due to the yogurt juice being discontinued so the creator changed the recipe for the appropriate substation for that ingredient. That is the only time substitutions should be made ...in my opinion
As a side note I have fed Bml but I'm currently feeding a different diet. I'm diet neutral for the most part but there are a couple I don't like at all. I won't argue or debate about them I just don't promote them like I do others.