Beneficial nematodes, replacement for ladybugs???

Okay so here's the deal.....I'm an outdoor grower and I know no matter what bugs will be around my plants so a bite from a leaf here and there doesn't freak me out too much, but I want to start planning for the worst just in case because my plants started flowering a week ago. I was searching around to see if there was anywhere around me that I could buy ladybugs other than the Internet, and I stumbled across these things called "beneficial nematodes" on home depot.com I've never herd of these little guys but they sound pretty cool. They are safe for plants and seek out to destroy spidermites, bacteria, and any harmful fungi. These seem like they are easier to get ,and are more effective than ladybugs. Tell me what you think I'd appriciate it.

I used them in an indoor grow to get rid of some bug in my soil. I never figured out what kind of bug it was, but it was small and came out after I watered and jumped around the surface. After I used the container, the bugs went away. I would use them again.

Thanks were there any down sides?