Has anyone seen this befor????

check it out Let Your Plants Water Themselves With the Perfect Amount « The Official Smarthome Blog - All Things Home Automation

i really dont think it would that good since it would only be measuring the moisture levels at that one spot where the thing is instead of the whole thing

Might be helpful with a 5 gal capacity. I'd have to refill that thing three or four times a day.

If you are growing in soil, you are going to have to cultivate the surface around the plants (no more than a half inch deep) so you dont have any dry pockets. If you want an auto-watering system, you should look into hydroponics.