In PhotoScan 1.1.5, given a model with topology errors (specifically duplicate/free vertices is what I was working with)
1) Choose tools, mesh, view statistics. Note number or errors. Click cancel.
2) In console, run the fixTopology function on the model.
3) The function thinks for a bit, but makes no changes
4) Go back to 'view statistics'. Error counts have not changed.
5) Click "Fix Topology". It thinks for a while. The text output on the console is different than for fixTopology()
6) Go back to "view statistics". Note that errors have been fixed.
Edit to add: This is very low impact for me, just wanted to make you aware of it.