Almost impossible to tell from the blossom. Most Apple trees have very similar flowers shape and colour.
Best way to choose a Crab apple is to go to a Nursery where they sell them. Go twice, once when the trees are in flower and then later when the fruit is on them.
Having said that. John Downie is a good reliable orange fruited variety. Evereste is good, but the fruit is small and bright red. Golden Hornet is good, small yellow fruits. If we were buying another we would go for one called Gorgeous