Are all shoe trees the same or are the brand name ones better quality?
If the material is the same then there should be little difference between brand name shoe trees unless they are a specifically shaped last for a specific shoe, i.e. when you buy bespoke shoes it is common place to recieve a pair of shoe trees specifically for those shoes as they will keep the shoe as close to its original and intended shape.
TIP: cedar shoe trees are the best for many reasons but bespoke shoe trees are often made from a range more luxurious woods for aesthetic purposes.
If you call Allen Edmonds (or this may even be online) - they have a "cheat sheet" that lists every width/size and what size shoe tree goes with it. I have 2 pairs of AE shoes and both have AE shoe trees in them - I like them a lot.