Modem certification rating

Hi,

I currently have the Arris TM502G modem that has a "Cert" rating of 3 stars.  What does the certification rating mean?  Is this modem current and able to support all of the internet features available to me?  I currently have the Comcast Performance plan with upload/download speeds of 16.44/5.33Mbps.  Is this a good outcome of this tier of service?  Is there another modem that would be better for this service?

Thanks,

Cheryl