[bunderbunder]

The cow pie is biased work.

The root problem with using meta-analysis is that it just wasn't designed to work with real-world science. It generally assumes that it's being applied to an unbiased sample of unbiased results. It's now pretty well understood that the published literature is really a biased sample of (oftentimes) biased results. No amount of selection criteria can fix that; the best you can hope for is that they will yield a biased sample of unbiased results.

I'm no expert on health science, I'm just taking potshots from the peanut gallery, but I'd guess it's pretty much always better to ditch the shiny mathematical bauble and its false promise of providing an easy, simple, objective answer to an inherently subtle and complex problem, roll up your sleeves, and get to work on a proper systematic review.