A networking group that lets anyone join who can pay sounds generous, until you are the third accountant in the room, watching a referral you could have handled go to somebody who joined before you.
Matrix is a single-seat group. One business per category. When a member needs a surveyor, there is one surveyor to send them to, and that surveyor is sitting at the table.
It has two consequences worth being clear about. The first is that a referral inside Matrix is unambiguous, so it actually gets made. The second is less comfortable: seats run out. If your trade is already in the room, we will say so when you ask.
We think that trade-off is the right way round. A group that fills every seat it can sell is optimising for its own income. A group that holds one seat per trade is optimising for the people already in it.