Other people are definitely allowed to charge money for help in obtaining or installing Let's Encrypt certificates. However, most of the tools for obtaining certificates don't charge money.
I have definitely heard about this tool before and I guess it's popular among Chinese-speaking users because it's available in Chinese, unlike some of the other methods of obtaining certificates. I could ask a Chinese-speaking colleague to look at it and give us an opinion about how useful it might be.
Let's Encrypt and ISRG are not affiliated with any of the tools or sites that help you to get certificates. The Let's Encrypt certificate authority has an open API allowing any software to request certificates.
There is a list of client implementations at
Unfortunately, most of them are not yet available in Chinese. One client that does have some official documentation in Chinese is acme.sh:
Whether this is useful to each user depends on his or her hosting environment (for example, acme.sh requires you to have shell access on your web server in order to use it in the most straightforward way, which some users have and some users don't have).