I had the displeasure of using this at a previous client. It's a good example of form over function. It looks decent, but is an absolute nightmare to use:

* No Markdown editing support, only wysiwyg. Certain Markdown control characters will start wysiwyg markup blocks but not stop them, overall making it terrible to use.

* Markdown imports are bad. Valid Markdown that renders fine in StackEdit has trouble when imported into Slab. Ended up using StackEdit to render to HTML and then pasting the HTML.

* No Markdown export, so you can't export the existing text in Markdown so you can edit it in a decent editor instead of the shit wysiwyg.

* No "save" button. It's supposed to save incrementally and I guess it also saves when you exit out of edit mode, but honestly I would not trust it on a flaky connection. Just give me a good old save button when I have real feedback when the document is saved in the form of a page reload.

* It lags. They have managed to make text lag. It's a sad but nevertheless very impressive achievement. I wonder how many NPM packages they have in their dependency graph. The entire product just feels bloated and you start being scared to click anywhere because it'll cause a good 1-second delay during which your CPU will be at 100%.

With these limitations I wouldn't take it for free, let alone 35$/month.