The new unfold mesh tool is a great start, I like the way that it reports before/after surface area, which tells immediately whether the unfolded facets overlap. I've used a UV mapper and mesh unwrapper called UltimateUnwrap3D, which only gives visual feedback of overlap, but which has three unfold paradigms that tear mesh edges differently, and which unfolds a subset of selected faces if the entire mesh object isn't selected, which I find makes overlap easier to interpret and rectify. The one drawback is that it's possible to select the same faces in a subset without realising, which means that the faces are unfolded twice, confusing the result.