Holder Status

Usually when you buy from the sponsor, the shares are no longer "unsold", and more important you no longer have the right to sell or lease without board approval (which the sponsor usually does have).
So, if you are looking at this coop purchase as an investment, it is probably not a good idea.

And, judging from someone I knew who a number of years ago bought a block of apartments in a condo, and who, sort of without initially realizing the implications, stepped into the sponsor position, that is something you REALLY wouldn't want to do.

Right, the state has all kinds of conditions for someone to qualify as a HUS. The current HUS has to sort of certify your bona-fides, and on and on. So, as the agent said, it's not worth it to the sponsor for one apartment.