Before the Markup Hero, I was using Snagit it for screenshots sharing for years but it doesn't mean I have not tried other tools. Based on my own personal experience what all I can say it Markup Hero going to be my daily driver for the following reasons
1. Universal annotations tool to annotate images, screenshots, URL's, PDF's, Docs, Spreadsheets, Slides, etc.
2. Annotations you make using Markup Hero are not usual annotations, these annotations are layered and editable, meaning that annotation can be edited even after sharing it (link will remain the same but image will get updated). In other words, Markup Hero has the capability for share once but edit repeatedly and go back repeatedly.
3. Layered annotations open all possibilities for real-time collaborative editing.
4. Bloat free editing experience!! You get only the tools that are required and useful. No useless features that are used once in a blue moon.
5. I haven't tried Slack integration but Markup Hero is available as a Drive Add-on and can be installed from the Google Workspace Marketplace. This means Markup Hero can be used directly from Google Drive to create and edit files. This also means that just one click and you are annotating any Google Doc, Google Sheet, Google Slide.

And here are things that wish to have in Markup Hero
1. It lacks proper file management. Considering the usefulness, in no time you are going to have so many screenshots in your Markup Hero library. You can tag images but cannot arrange them inside a folder. Hopefully, they bring this feature before it's too late to arrange thousands of images.
2. As it doesn't have folder creating functionality, it's obvious that it also doesn't offer folder sharing and folder privacy functionalities.
3. Initially I thought they have everything for such tool but soon I realized that they do not have the Blur tool, and Blur tool should be implemented differently so others can't remove it while collaborating.
4. Such a useful and beautiful tool and no team functionality? It's there in the roadmap. This deal launched without a team plan and no stacking option, does this mean Markup Hero Lifetime deal is not for the team plan?
5. No custom hotkeys, no scrolling screenshots, no multi-select for annotation objects, no custom branding, no custom domain.

Please do note that the product is evolving, and they have a solid roadmap, some features are also inside the planned section of the roadmap but without any timeline. Hopefully, all missing features arrive soon and Markup Hero becomes a game-changer. ;)

Wish you success!!