Nice site. They go into a lot of details throughout their site, but there's still the nagging question;
Unsuitable for e-commerce — free certificates are not recommended for securing credit card and personal information on e-commerce websites.
They talk about trust of the visitor, but at that point aren't they talking about the badge someone might put on their site (this site uses Comodo SSL)? They're not really talking about the security of the certificate at that point, they're talking about the brand name of the SSL.
As far as the limited terms and re-issuing every 90 days - most places have this automated, so it's not really a big deal.