I can only give you my opinion: the Start/Stop feature is exactly for this type of usage. Gas mileage is lowest when stop/starting a great deal- the S/S feature assists the owner of the vehicle to counteract poor gas mileage.
2014 BMW 528ix M Sport- Space Gray Metallic, Mocha Nappa Leather, Anthracite Wood Trim. Packages: ACC, DA, DA+, Lighting, Luxury, Prem, H-K SS, SAT, Rear Shade
2013 BMW X3 28i M Sport - Deep Sea Blue Metallic, Sand Beige Nevada Leather, FS Wood Trim, HG Roof Rails, and BMW Apps. GY Eagle LS 2 All Season Tires.
Packages: Cold, Con, DHP, Prem, Premium Sound, Tech