Just because they are “not accepting new members” doesn’t mean they won’t search for you. It just means that they are full and aren’t obligating themselves to you.
You choose 2 matchmakers, those matchmakers are obligated to search for you once a week or something (otherwise they get kicked off the site, I’m not sure the rules exactly).
But any matchmaker can do a search and suggest shidduchim for you if they want.
And you will come up in their searches when they are working on others (if a matchmaker does a search for a boy, your profile might come up as a possible match based on the database’s algorithm and then the shadchan can suggest the match whether you are “in their network” or not).
Bottom line, sign up and see what happens. It’s not a scam.