M&MS for SLH was a terrible deal for Hyatt members. M&MS is basically just a booking agency, and all they're doing is taking a commission (and presumably kicking part of that back to Hyatt). I have a booked-direct rate with Bellevue Syrene in April that was about 150€ per night cheaper than M&MS. Which tells you something about the commission they're taking.
An utterly worthless partnership so far as I'm concerned.