SPP Harvester by OnMarket, page-602

When it comes down to it, it's the efficiency & service that's far more important than whether you pay $5 or even nothing to sell.
If it takes them 1-2 weeks to get your shares on your account you could lose a lot more than a few dollars extra brokerage.
We've seen that already on SPP Harvester & you wouldn't want to be selling after they've started offloading.
Unfortunately there's no way of knowing ahead of time unless you're a customer & been through a SPP with them.