The Crab apple species are usually grown as bonsai mainly for the flowering and fruiting potential.
We are not sure of the species of this example it having come as part of a collection we purchased last year. No flowers this spring but that will come with a bit more maturity. They usually flower quite prolifically once they start and assuming the flowers get pollinated with follow up with the crab apple fruits. This tree is 52 cm. in height with branches spreading to 40 cm. The trunk diam at the base is 2.5 cm. More fine branches are needed which is an exercise in growing and selectively pruning. The pot is a round Mica plastic bonsai trainer that measures 28×9 cm.