It's definitely interesting to see how people's workflows can be so different, I get by with at most ~10 tabs, and close things as soon as I'm done with them. At the end of the working day, I prefer to have at most 2 or 3 left. I sincerely start to experience existential anxiety when the number of tabs goes up too much :-P. Probably related to some subconscious feeling that I need to 'do something' with all these tabs and when they increase in number it starts to feel like I'm 'running behind'. Different people, different workflows, that's perfectly fine.
What I don't really see is why this service needs to exist to solve that particular problem (browser gets slow because too many tabs), because IMO that problem has already been solved very well by most decent browsers. They just swap out the inactive tabs and are able to restore them fast enough even on low-end systems, as long as they have an SSD. Inactive tabs that are not swapped out don't take a lot of CPU resources either. This service sells you a cloud browser with 16GB of RAM, which is pretty much the norm for laptops and desktops now, so it's not going to save you much if 'too many tabs' is causing slowness.