There are many third party trusted Certificate Authorities such as GeoTrust, Comodo, Thawte, RapidSSL, who offers free SSL certificate for 30 days and 60 days. And, after trial duration and they will insist you for standard purchase at discounted prices.
Find out SSL certificate authority reviews, SSL installation guide, SSL comparison, SSL certificate errors & solutions, SSL news at AboutSSL.org
Lets Encrypt SSL certificate will be available only for 90 days of period. To active again you need to go through issuance process again and installation process as well.
This is quite boring stuff, as you need to re-active and re-install SSL certificate on your server.
Better to buy SSL from other Trusted SSL certificate Authority which available for 1 to 3 year option.
One more disadvantage of Let's Encrypt SSL Certificate is its only available for domain validated websites, so for business, e-commerce, banking and other platforms Lets encrypt is not available.
Lets encrypt will work find, but they are offering SSL for 90 days only. That means you need to reissue your certificate for each 90 days of interval. This will become more hectic. And if you forgot to reissue your website will no longer be encrypted.
It will be better to get SSL Certificate from trusted SSL Certificate Authorities.
Find out SSL certificate authority reviews, SSL installation guide, SSL comparison, SSL certificate errors & solutions, SSL news at AboutSSL.org