Yes it is legal or illegal?
It is legal.
Legal activations are tied to serial numbers (or Adobe IDs in the case of the Cloud).
Trials have no serial numbers so they are not tied to anything other than a 30 day time limit.
Each trial will be treated as a separate, standalone installation (so you can install as many Trials as you like, once per computer for 30 days until the Trial expires) until you license it via a serial number or a Cloud membership.
Once licensed (via serial number or Cloud) the two activations per license applies.
The OP's question:
My reply in Post #1:
Yes, it is.
…and when you buy the final version, you can do the same thing, since the license is for one user on two computers that are not used at the same time.