No, Seer does not contain any malware, spyware or adware.
Seer has been a lot of media coverage, including The Verge, Softpedia, Lifehacker and etc.
Seer doesn't collect anything. Seer can work perfectly without network access.
Seer - How to add a plug-in
Seer - How to add a control-bar app
Seer - Translators
Designer