It depends on the drug. Shipping is enough to make it more expensive than Costco or GoodRX in some cases. YMMV.

It would seem to me the appeal of this service is not saving x% on average but avoiding paying x000% more for some niche needs.

This is where it is difficult to judge from where I see it. The last company I worked for had great insurance, really great insurance and this CostPlus in most areas can't beat what I would pay through insurance. However, I am in a new job where the insurance isn't as great, so maybe CostPlus may come out to be cheaper? I havn't delved too much into my current insurance to know yet, but it definitely isn't as good as the insurance I got through my last employer.

"this CostPlus in most areas can't beat what I would pay through insurance"

But are you taking into account how much a month you are paying into that insurance when comparing the two?

If CostPlus is coming close to what you are getting your prescription for with a paid into insurance plan, than I would call that a win for those without insurance.

Might be worth looking at lowering my own insurance coverage to one that might not be that great for prescription, as long as costplus and costco type places come close to after insurance priced meds.

I order a steroid cream and its significantly less than Walgreens for the exact same thing. Just my 1 data point.