SSL (which stands for Secure Sockets Layer), is a protocol that's used to protect and secure transactions between destinations on a network. SSL enhances a site's security by providing two very important features, namely; authentication and encryption. Recently, SSL certificates have become a must have attribute for sites that want secure dedicated server web hosting, and for sites that handle any kind of payment related information or personal data, you do need an SSL certificate. Also if your site contains login forms where the users log in with a password and a username, you should protect the information with SSL. This helps prevent any malicious actors from stealing the login information, or eavesdropping. That being said, lets now take a look at the differences between Free open source SSL and commercial SSL certificates;
Free Open Source SSL
Free open source SSL certificates protect sites by providing a basic level of protection, therefore shouldn't be used for e-commerce or banking transactions. These types of transactions require a much higher level of security that's provided by commercial SSL certificates. The free SSL certificates are also not automatically trusted in all of the modern browsers. The browsers may display a warning message which tells the visitors that the cert isn't trusted. In addition to this, free open source SSLs aren't compatible with Microsoft based servers such as IIS and Exchange, until the cert is originally created on a Linux based system.
That said, it's important to note that some free SSL providers such as Let’s Encrypt, usually set limitations on the SSLs renewal process. Let's Encrypt SSL certificates are only valid for about 3 months and need to be renewed frequently. Let's Encrypt also doesn't have adequate staff available to assist with installing SSL certificates, and this can be a major issue for business owners and professionals who must get a website configured and working quickly.
Commercial SSL Certificates
Unlike Free SSL, commercial SSL certificates essentially have a warranty of the specified sum in case of any breach of security. Commercial SSL certs are also highly trusted in most of the modern browsers, and there's no warning message that's shown to users. In addition to this, commercial signatures for the SSL certificates allow users to easily verify that the site they're viewing is operated by somebody who's in contact with the person who registered the domain name under which the site operates. When it comes to liability protection, you are going to get much better services with Commercial SSL certificates than you would with a free open source SSL.
That being said, it's important to note that most of the commercial SSL certificates issuers provide Wildcard SSL certificates, which makes it easier to work with sub-domains. Wildcard certificates cover your primary domain name and all the affiliated sub-domains; this is great if you are running a business with many different servers.