If the tenants go to Econsave often and not using MRT daily, then they can opt for MM and get a cheaper rental.
On the other hand, some tenants who use the MRT everyday, they are willing to pay slightly extra to be nearer to MRT station.
Look at Aster, Maxim Residence, Maxim Majestic, Annex, you might see many units here, but all of them are not same. Exact location different, facilities different, layout different, distance to MRT different, etc. So tenants/buyers in the future will rent/buy based on what matters to them, whether they want to stay nearest to Econsave/MRT/shop offices etc.
This is different from having 4000 units within the same site, with the same layouts, same facilities, same finishing. Then the competition is very high because it is hard to differentiate between the units, except the preference for the level and facing.