I use a really good moisture meter, it's the finger next to my thumb.... No batteries to wear out, no problem reading the gauge.

I think the electronic meters are crap as I've seen too many people screw them up. Just make sure that if you're growing inside that you have holes in your buckets / containers for drainage. If your outside take a shovel and dig a small hole as almost everyone who's plants were small this past year (outside) were not giving them enough water. You may also want to look at products such as Water-Keep to help eliminate water stress. Maybe you'll have some 10' monsters next year!