Based on the examples provided in their announcement, the discounts are on the order of 5-7% so one would have to both spend at least $800-900 per year AND not be very good at timing their purchases to catch the regular sales to make membership worth the cost. I do fear that Defender’s great sales might eventually become fully or partially limited to paid members.
That said, even though I don’t meet the spending threshold and won’t sign up for the membership, I think this is ultimately a smart move on Defender’s part to “lock in” some of their customers who meet or are close the spending threshold.