Start with what 'all-in-one' is claiming
The first question to ask is whether the food is genuinely complete for your reptile's species and life stage, or whether 'all-in-one' is describing a general supplement dressed as a diet. A food formulated for a bearded dragon does not automatically suit a leopard gecko, and a juvenile's needs differ from an adult's. Ask what the food was designed to replace: some products are honest staples, others are top-dressings meant to sit alongside live food and greens, and the label language is often vaguer than the shop's pitch.
Ask about ingredients and the nutrient balance behind them
Ask what the main ingredients are and where the protein comes from, and be wary of a list led by fillers for a species that eats insects or whole prey. Then ask about calcium and vitamins specifically: does the food contain calcium in a useful balance with phosphorus, and does using it change or remove the need to dust live feeders? A shop that stocks the food should be able to answer plainly or show you the manufacturer's analysis; shrugs at this point are information in themselves.
Ask how it fits the rest of the diet
Even a sound formulated food is rarely the whole story, because variety carries nutrients and enrichment that one product cannot. Ask what the shop would still feed alongside it — which live insects, which greens, how often — and how the food is served: rehydrated, dry, or mixed, and how much per meal for an animal of your reptile's size. Ask, too, what evidence sits behind the formula, since feeding trials and a published analysis carry more weight than testimonials on a tub.
Ask what a week on this food actually looks like
Ask the shop to walk you through a realistic week: how much of the product your reptile would eat at a sitting, whether it is served at every meal or some, how an opened pack is stored, and how soon it must be used up. Ask whether it needs anything added at serving — water, a dusting, a topper of live food — because those additions are part of the real routine the word 'all-in-one' is claiming to replace. A recommendation that survives these questions in detail is a very different thing from one that survives them in slogans.
Ask what happens if your reptile refuses it
Refusal is the question shops least expect and owners most need answered. Many reptiles, snakes above all, simply will not recognise a processed food as food, and some lizards take weeks of gradual mixing before accepting one. Ask whether you can start with a small quantity, how long an opened pack keeps, and what the shop's return position is if the animal will not touch it. A refusal plan protects your wallet and, more importantly, means your reptile's feeding never depends on a single product it may reject.
Jot the answers down while they are fresh, because the details blur by the time you are home deciding what to serve. For a further question once you are home, put a follow-up question to KinsLe's Kinny; he answers using the KinsLe Answers library.