I wouldn't consider 227 to be very discreet, bro. The only thing they have that helps in that department is the back entrance, but the problem is their location has very heavy foot traffic all day long. There are always people at the front and the back. That laneway where you enter the back entrance is right near the incredibly busy pedestrian crossing that leads into Broadway shopping centre.
MAC is not very far off. Extremely heavy foot traffic location, bloody bus stop always full of people out front. The only thing that might help for MAC in terms of being discreet is it is so busy that you might easily get lost in the crowd.
Out of the 3, SBM gets my vote for being the most discreet. Location is in a semi residential area, on a small laneway with hardly any foot traffic. The shop only has 1 entrance (?) but that's fine for me because it's a bit "recessed" from the main street. Never crossed my mind to look for a back entrance because the front is discreet enough.
Good luck bro.