There is no doubt that a Free SSL is a convenient option to have in a hosting account. The level of encryption provided by a Free SSL is the same as what you would find in a paid SSL.
However, it is worthwhile to note that free certificates use SNI without a dedicated IP. This means that multiple domains can share an IP address and still use an SSL. It should be noted that this type of certificate does not have the same level of acceptance as an Advanced SSL with a dedicated IP. This is because SNI is a relatively new extension and is only recently receiving widespread support across browsers and devices. Some combinations of older browsers and devices may not accept a certificate that is using SNI.
What is SNI? SNI stands for Server Name Indication and is an extension of the TLS protocol. It indicates which hostname is being contacted by the browser at the beginning of the 'handshake'-process. [Server Name Indication - Wikipedia]