I knew other grad students who'd say, "oh, it's a meta analysis" and then toss it in the bin. But in recent years I've met people who worked on boards for cities and hospitals where they dug though a lot of papers and wrote detailed meta analysis about the larger body of work. They'd comment on things that seemed consistent and inconstant, and tried to help others make well informed decisions.

With a meta-analysis, you do have to look at the whole thing. Phrased like, "when controlled for.." you can't control for some things over 10 different studies. You need to read how they attempted to control for things and why the came to their conclusions.

They are still valuable and you shouldn't just chuck them in the bin.