Stackby is a powerful database tool. Would I say it's worth replacing Google Sheets with this deal? Yes (only if you don't intend on going anywhere near the limits of this deal).
I do not really like the deal structure though. I wish there was less emphasis on number of users or storage limit and more on the stuff that matters like # of workspaces and stacks and rows since that translates into a very hard ceiling inside the platform I can't circumvent in some way. I can share my login or host storage on the cloud and link to it inside Stackby, that's a hassle but not a problem.

Pros:
- Some powerful features if you know how to properly use a database.

- The UI - it's pretty easy to look at due to its simplicity* (not to be confused with an absence of powerful features)

Cons:
- The UX - the curve is far too steep for probably most of the folks here on AppSumo (not trying to offend anyone, it's just not intuitive to capture a wide enough audience, you have to LOVE data to grind your teeth and get through the weeds with this)

- It's far too rigid - there are asinine hurdles you have to jump through to set up your data. Trying to get started in any other views that aren't "Grid" is impossible unless you have certain columns in place beforehand, for no reason whatsoever. I have to have a Correspondents column in my Grid, but clearly when I get to Kanban, it doesn't make a difference as they're shown as unassigned on the left. Stuff like this is really bothersome and the exact reason I hated Jumppl. RIGID SOFTWARE IS BAD SOFTWARE!!! You can't change the table's primary field easily after you've entered data, I should be able to drag and drop whatever I please to make it the primary field, don't force me to choose a field type and stick to it for the lifetime of that data. Also seemingly can't delete rows once you create them?

- With the limits that are imposed to you per stack, it's a shame that you can't link to other stacks inside one workspace...

- The integrations as of right now are meaningless to me, which is tragic - I hope Zapier will fix that. I wish there was the ability to connect directly to a service's API so I didn't have to wait or rely on Stackby to create what I need. If I can grab the code from somewhere, let me connect independently.

This should NOT be considered for project management (sorry). It's just too rigid to manage and so much of it is going to have to be done in views you might not be comfortable with or that force you to have X or Y qualifiers present in order to even access it. If you want something similar, check out Infinity (and no, I have zero affiliation with them) which is in this trinity of Airtable and Stackby when directly comparing products with a sort of similar interface, but allows FAR more flexibility, customization, and complete control - it's still young and missing things such as these APIs but considering none that live inside Stackby are helpful to me, I can't give it a point for that either.