Hello @Anna Golitsyna!
the 3rd example is 1 class that contains 2 basic functionalities:  A Server and a Client.
The system you want to control runs the ClassMethod Server.
- opens an IP port and listens for orders, execute it, and continue looping.
- it is typically started in the background during  system start (from %ZSTART.mac)
This is the "hidden Login"

The (Classmethod) Client connects to the listening port and sends a request and gets answers.
The structure of Requests and Answer is up to you and makes sure you have always control
over what should happen on the remote system. As your  "Listener" is active already there
is no need for any further login. But you are of course free to implement it on top of this basic mechanic.

The major impact is the default collation for CACHETEMP/IRISTEMP.   This may affect sorting!

There is my related question Multi Language Sort  

@Vitaliy Serdtsev provided an excellent solution as reply to the problem
including a detailed example of how to cover solve the issues I found
with basic features already available in Caché since almost ever(?).

Besides the functionality and speed that you mentioned already,
there come other factors to my mind. Just a few from the hip:

  • Portability: Moving a Caché/IRIS DB from one system to the other is as easy as a file copy. And this goes across most actual operating platforms on local HW or in the cloud, from Win to *X and back
  • Flexibility: Splitting or extending your DB if you run out of disk space has no impact on the applications. Vertical or horizontally scaling is a standard feature
  • Connectivity: especially with IRIS you have a huge range of adapters and interfaces available that allow access not only by SQL but also by Objects without any need to separate the data accessed from each other.
  • Openness: You need a private SQL Function or SQL Procedure because Standards don't fit?   No problem: Just add your self modeled ClassMethod and you have it done for both SQL and Object access.  

As I mentioned already in a different place: The only limit is your own imagination.