Does Tiger Motor MN5212 compatible with HOBBYWING XRotor 40A ESC?

Yes, it is compatible with Tiger Motor MN5212.

When using the 15 inch or 16 inch propellers, users can use our XRotor 40A ESCs.
When using the 17 inch propellers, users can use both XRotor 40A and XRotor 50A (while we recommend using the latter).
When using the 18 inch or 20 in propellers, users can use our XRotor 50A ESCs.

Generally speaking, the actual amperage cannot exceed 2/3 of the nominal amperage of the ESC.