As far as reliability goes there can't be any difference since the Covad service resold by Cyberonic is still the same Covad service as far as the IP connectivity is concerned.
The main differentiators are add-on ISP services that Covad-direct customers receive from Covad servers and Cyberonic customers get from Cyberonic. This is an area where Cyberonic in the past has gotten poor remarks from users that require these services from their ISP (e.g.: unreliable email server, no usenet news server).
Another difference is that in the case of problems a Covad-direct customer calls Covad for problem resolution and a Cyberonic customer has to go through Cyberonic support to open a trouble ticket. I don't know how that works these days, but in the past Cyberonic support was not open 24/7.
Covad service can be provisioned as PPPoE or PPPoA (seems to depend on region, but sometimes the customer can choose between the two) regardless whether you are getting dynamic or static IP address(es).
On the Cyberonic-Covad service with static IP addresses there are no port blocks as far as I can tell. Some ISPs differentiate between their dynamic and static offerings and have port blocks on dynamic service. I don't know if this is the case with Cyberonic or Covad.--
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