Controller for maintaining nutrient mix/levels

Has anyone deployed a controller/EC probe/peristaltic pump hydroponic controller?

There’s several commercial ones that’d work in a small scale grow, but they’re aimed higher in the market ($2000 for a controller & 3 pumps). (See, e.g., Bluelab Pro Controller)

There’s also several open source projects to do this, aimed at hobbyists and engineers using rPi or Arduino. (See, e.g., Atlas Scientific)

Curious any experiences you’ve had.

For those less familiar, the idea is that the controller samples EC, and if EC is too low then it’ll add a smidge of nutrients via peristaltic pumps (in the correct ratio for the current week or whatever), measure again and repeat. I’m kind of worried about roll-your-own solutions – error conditions abound which could kill the plants.

(I already have a separate pH controller which works the same way, but just one solution and it’s easier.)