I am designing one. Been about 2 years now.
It has peristaltic pumps with 0.5ml accuracy or 1%, whichever is larger. 7 inch touchscreen, 1 year of data on the device, PH measured to 0.001, TDS measured to 1, monitors RH%, air temp, tank nute temp, modular so you can get as little or as much as you need, and a relay box to operate up to 8 5A mains devices (relays are rated at 10A but inductive loads like lights are rated differently)
It can keep your PH regulated to a range of +_ 0.0125 and I am finding the extra stability is very liked by the plants.
If you look, you will see that 5.9 is at the top of the graph, 5.8 is at the bottom, and the graph covers days.
Years ago when I bought my Intellidose, I found the difference in yield between having one and not (due to limited access to the plants) paid for itself twice over in the first cycle. When it died I thought "I could make one of those, it can't be too hard" and now here I am two years later...
I still have many months of work on the coding side of it though so it will not be available any time soon. It has the function it needs, I want to make it easier to use and allow the user to make setpoints through the interface and other features.
I used to have the intellidose, which can connect to a PC so you can see graphs of your readings, and I found that good. I have not tried the bluelab one. TBH any doser is a shedload better than no doser.