Q1: It seems that it is rather old technology. I wonder whether it is still effective for monitoring current situations or not.
Les> It is old technology. The advantage is it is standard over almost 20 years worth of data. Newer technologies such as Akamai (see https://www.akamai.com/us/en/our-thinking/state-of-the-internet-report/state-of-the-internet-connectivity-visualization.jsp which goes back quarter by quarter to 2007 with Akamai download speeds by country with a linear y scale. The full report is at: https://content.akamai.com/pg8228-q4-2016-soti-connectivity-report.html) and perfSONAR only have data going back a few years. Also bear in mind the analysis tools do not support IPv6 (the measurement agent does support it).
The traceroute.pl tool (for remote traceroutes and pings) supports IPv6, is part of perfSONAR and is independent of PingER. Even if you don’t install a PingER MA (pinger2.pl) I would recommend installing these.
Q2: I'm afraid whether such monitoring will do harm to the security and safety of our own hosts and related facilities or not.
Les>There has been no evidence of this. Considerable thought was given to this in the implementation.
Q3: I feel that we can do some useful things using the data monitored. Is it free to use such data if we participate in the monitoring? Furthermore, can we use all the data or only limited usage of the data.
Les> The data is public and free to use. You can use whatever you want. The data is updated daily.