700PPM on a Hanna is 1.4EC. 700PPM on a Truncheon is 1.0EC. Thats a big difference IMO especially for DWC.
An automated pH doser is good if you have a large res or an RDWC. Ill never grow without one and bought a second one last week.
If I knew arduino id build my own because there are some things I dislike about the manufactured ones.
The cheap way is a DC peristaltic pump and a MC122 controller from Milwaukee. These can be had for a bit over $200