Commercial ones as you called them are TRUSTED. Therefore a browser won’t be suspicious when it receives it, but when it receives the self-signed one it’ll warn the user that the it has no way of trusting the site, even though the same SSL Protocols can be employed; the security isn’t downgraded but can be an annoyance and could deter clients if it was a public Website. For private projects there is nothing wrong with self-signed as it is still same security. There are free ways to get Commercial SSL Certs such as StartSSL or WoSign: https://buy.wosign.com/free/

is this trusted company ? https://buy.wosign.com/free/ did you try? looking like some Chinese. I think better to buy SSL with domain and from hosting provider. thanks for help guys