I am an automation expert. I develop embedded systems, and I have a passion for monitoring and automating everything. I make my own devices AAND I buy other people's designs when they are interesting because they may have 100 people writing software and I am just me, so even those of us that can make our own can see value in spending money to buy someone else's efforts.
I have every sensor you can think of already, many are different brands and models so I can compare and contrast the readings. The pulse zero doesn't have anything I don't already have except one thing, the app. AND to get all of these sensor types running will cost more than a pulse zero if you put any value on your time. If you calculate the value based on the cost of my time, Pulse has paid me at least a few thousand dollars in value by letting me buy from them. The math isn't hard, but you should do your own.
When I want to check on things, the pulse app puts it all in one screen. Sure I can check all of my other sensors, but the pulse is like an executive summary with a detailed histogram all on one screen for rapid information uptake.
If you have everything already, you will find this useful. If you have nothing and need a starting point, you will find this invaluable.
And there is a lot of value in having the VPD math done for you, you can't go by humidity alone.
And the whole room needs tuning as the grow progresses... A roomful of young plants has completely different needs than a room with several plants nearing harvest. Keeping the VPD in balance is easier when you have a histogram to tell you not just how it is now, but how it was for hours days and weeks... VPD changes constantly as your systems do their jobs, being able to see the full range of your grow over time helps you understand the simple things you can do to influence the conditions.
Why you might not buy a pulse zero? Because you buy the other pulse products instead? Need more sensors? PH co2? Pulse has those too for the more sophisticated grower.
Got my eye on that continuous ph meter when I upgrade from central distribution dwc to chilled/circulated dwc... I need to figure out how to grab the ph and use it to titrate from automated up/down dispensers... Then there is the EC probe, don't wait for the plants to start calling you Seymore. There is always something else to automate.