Starting with some disclosure that Storeplum is offering some additional perks for leaving a review. While I'm going to take advantage of that, this is my honest rating and review.

I think Storeplum is the closest Appsumo deals have come to a solution for those of us who want a quick turnkey SaaS took to set up multiple online stores, want features but not every complex bell and whistle, and then to integrate them into our sites with CNAMEs.

The good:
✔️ They added support for digital products BEFORE the LTD ended. This alone got me to move from Tier 1 to Tier 3.
✔️ You (like me) want to naysay the arbitrary limits on lower tiers... but seriously, how many of our stores really ever get to $500k/year? If a lot of them, you're doing better than me... congratulations. (Over the limit seems to be a 2% commission.)
✔️The backend is well organized: Customers, Products, Shipping, Orders, Discounts, Storefront
✔️Plans to go headless for those who may want to grow a bit down the road. Although... plans are just that, plans.
✔️ Creates a list of abandoned carts and contacts for you.

If you don't want to configure everything (BigCommerce, WooCommerce, Prestashop), want to just create an easy store (like Etsy, Gumroad, etc.), and don't want the recurring costs (Arastta, hosted versions of any of the above, etc.) then this seems to be the LTD winning solution at current.

Now some of the questionable.
❌ I'd like 10 stores instead of 5, but yeah, I'm greedy that way.
❌ The store designer is clumsy and slow. Just rendering in real time and posting publish updates to Vercel it seems. I hope this is improved over time.
❌ Can't ever change your store theme. Also can't seem to delete a store without involving support, hopefully you don't lose a store from your count when you do. These are pretty major downers, if you're looking for some.
❌ If you're looking for an all-in-one site, store, blog... there's no blog feature, but you can do everything else.
❌ The product management and customer management is a bit barebones, but I suspect this will improve over time.
❌ Doesn't really do anything with the abandoned cart info. You have to do it by linking to your outbound email service.
❌ No dropshipping, but they indicated they'd consider it for the roadmap.
❌ Store doesn't seem to be able to include affiliate links... only first hand physical and digital products.
❌ Logins are extremely weird. Each store gets a short key-phrase you have to memorize or store that goes with your user/pass. I've heard managing admins is a bit clunky and they're creating a super-admin role to make it easier. No idea why the key-phrase matters, I'd rather have regular 2FA.

With this tool, I could go on with both the benefits and concerns, but I'm starting to see that the team is responsive, plans on improvements, is starting to execute those plans (digital products), and listens to user feedback.