It is not a puppymill - they are a rescue group.
Listen, someone will always say something negative about a rescue. There are holes in everyday life let alone a rescue. Everyone has an opinion about something. You need to find out if this is your dream dog.
Connect with them by phone. Speak to them and ask lots of questions. You will get the feeling on whether you want to deal with them or not..but at the very least give them or any other rescue a chance.