Vehling was a professional chef, not a scholar of Latin, and his grasp of Latin was limited, so his translations are not good. Also they are not based on the earliest available copies of the Apician cookbook. Instead, he used humanistically "enhanced" Renaissance texts. And he didn't understand the history of the various editions he was looking at. Thus Vehling's translations are full of gross inaccuracies. When his book was first published, readers had little access to anything much better. But today there are quite a few much more accurate translations, and more accurate translations lead to more accurate interpretations, when one wants to cook a recipe.
I won't even go into an analysis of his faulty translations, but, assuming most buyers want to cook food of the Roman Empire, I'll go straight to examples in his worked-out recipes...
Vehling uses a roux (a technique in which flour is browned or at least lightly colored in hot fat before having the fluid stirred in) to thicken sauces in many of his recipes. This technique was not common until the 17th century. Clearly the Romans used other techniques, and we can use them, too.
Vehling includes vegetables not known in Europe even in the 15th century, let alone during the Roman Empire, such as French beans aka green beans aka string beans (when the Romans used green fava beans, quite a different item), and bell peppers and kidney beans and pumkpins (which are all native to the Americas, unknown to Europeans until the 16th century).
In one recipe he even substitutes pate à choux (used for things like eclairs and cream puffs) for spelt or emmer grits (early forms of wheat)!
Additionally, he substitutes "broth" for "liquamen", that is, fish sauce, one of the hallmarks of Ancient Roman cuisine!!!
In fact, in many of his worked out recipes he "corrects" the original recipe to make it more like modern European cuisine, losing the flavor of the original and destroying its Roman character. Some of his worked out recipes are so transformed as to be nearly unrecognizable when compared to the original recipes.
If there were no other translations available, Vehling might be useful. But there are. And Vehling is misleading, erroneous, and wrong. Get a better book.