How ready is the current fusion reaction technology for the mass production of electricity? Could you give a clear summary statement about the maturity of the controlled fusion reaction technology and its readiness for the mass production of electricity? There are many articles on internet but I am lost in how to read them (e.g. https://en.wikipedia.org/wiki/Timeline_of_nuclear_fusion, https://en.wikipedia.org/wiki/Fusion_power) and which sources can be trusted.
 A: ITER is world collaboration and is projecting to start demonstrating energy production:

First Plasma is schedule for December 2025. This will be the official start of ITER operation.

There are 35 nations participating in ITER including the US. The site is reliable and official.

The ITER Members China, the European Union, India, Japan, Korea, Russia and the United States have combined resources to conquer one of the greatest frontiers in science—reproducing on Earth the boundless energy that fuels the Sun and the stars.

There are also a number of other fusion technologies in development, that may prove in the future to have an advantage over the Tokamak design of ITER.
Aside:
ITER is taking a long time to develop, not only because of the difficulties in construction and handling plasma at high temperatures  but also because it is a group bureaucratic effort, imo. They explicitly, when setting up ITER stated that they did not want to create another CERN, and imo, that was a mistake. CERN developed fast in technology because the engineering was not dependent on decisions of hundreds of home institutes. It had a central planning and budget, and freedom for planners to choose the best engineers in the open market. If the LHC were waiting to be built by the 3000 +3000 physicists of the experiments, the Higgs discovery would still be far in the future, imo. 
A: If you permit, it is more easy to answer the question: Why, to-day, controlled fusion does not produce mass electricity?
1 - It is not possible to obtain actually plasmas stability for a long time. As I know, the best time is 210 seconds on a french machine Tore-Supra. It is expected to obtain 400 to 500 seconds on the international ITER machine under construction. Stability needs big machines. Big machines are costtly. If a production mass electricity machine could run by periods of 10 minutes, it would be a success.
2 - To-day, it is not possible to produce more energy than what is used to heat plasma. It is expected to obtain 400 to 500 MW of fusion power with 40 MW for heating with ITER.
3 - It is necessary to find, to study materials "facing the plasma" wich could resist to heat power and high energy 14 MeV neutrons flux wich tend to destroy materials during a realistic time of production. Actually, these materials do not exist. A high power source of 14 MeV neutrons must be constructed in Japan to test possible materials.
4 - It is necessaty to prove the self production of tritium (which is part of the fuel) from lithium: an important technical step.
There is a very large gap beetween our "laboratory" machines and a future mass electricity production machine.
Numerous results are waited from ITER which would be in operation in 2025, full power: 2035.
The next step is "DEMO" a small prototype of a production machine (2030 - 2060?).
And possibly, a production mass electricity machine ( 2050 - 2080?).
Nobody knows to-day the real planning ...
