CertSimple will be shutting down on January 30 2020. Read the announcement here.
Let's Encrypt is a great, free service that provides free DV SSL certificates to allow people to encrypt the connection between their browsers and your domain. Since DV certificates don't try and prove who owns the certificate, DV certificates are issued almost instantly to any domain.
CertSimple doesn't sell DV certificates.
CertSimple only does EV certificates. EV certificates verify the legal identity behind websites. In most cases it's a company, sometime's it's a registered charity, or a sole proprietor, or one of the partners in a partnership. DV certificates don't verify anything except that you have purchased a domain - again, this is by design, and allows DV certificates to be produced automatically and for little or no cost.
If you want to prove who you are, because:
Or any other situation where your customers need to know who they're communicating with, give CertSimple a go.