we do all have different opinions on diets, how ever most of us agree that they need to be ON one. Which one is entirely up to you and your gliders. What works for me may not work for you... there is no best diet, the best diet is the one that your gliders eat well.
Some diets you can only get online so if your not willing or able to order online then those diets won't be a good choice for you. Hpw critter love, tpg and a few others you can only get some or all the ingredients online.
Bml you can usually find all the ingredients locally. But, the fruit and veg that need to be fed with it is very specific.
Cost is another factor, what you can afford to always have on hand.
ease of making the diet, some require a blender, some require a lot of chopping of fruits n veg, some just require water.
What your glider will eat. There is no way of knowing if a glider will eat one diet better than another until you actually try one of the diets.
What kind of "powders" calcium vitamins largely depends on what diet you chose. The diets are specific about ingredients and should NOT be substituted. If it calls for Repcal calcium use only repcal calcium etc...
the ingredients have a purpose, and have been formulated to keep the over all diet balanced so the glider gets what they need.
Yes absolutely research, but these are some things to consider when chosing a diet.
If you are planning on getting a cage mate, please consider neutering your handsome lil man first