BRS has great prices on a lot of stuff but they're sometimes higher than MD so although you're getting free shipping you are going to wait a lot longer and you might be paying a higher base price, really depends on your total order. Sometimes Amazon may be a better option if ordering 1 item and need it faster than 5-7 days (what it usually takes to get to me).
A recent example I came across was when I was looking for MicroBacter7
Marine Depot: 250ml: 7.64 + Tax 8.25 + 4.99 shipping / 500ml = 13.49 = 14.57 + 4.99 shipping
BRS: 250ml = 9.99 (no tax/shipping) / 500ML = 16.99 (no tax/shipping)
Amazon: 250ML = 13.83 + Tax 14.94 (free 2 day shipping with Prime) / 500ML = 15.37 = Tax = 16.45 (free 2 day shipping with Prime)
Note: BRS Rewards Points may make it worth continuing to order from them vs. MD or Amazon.