Quick review.
I had 110GB worth of photos, almost exclusively in iPhoto and duplicated in Photos. I installed the app, adjusted the sliders slightly, ran the comparison and it came back with perfect results in maybe 10 minutes. IMPRESSIVE! Instructions to move forward with actions (ex. deleting duplicates….. duh) are very clear and straightforward.
One thing of note - deletion is guided, but not automated. You have to take manual steps to actually remove the files and regain your HDD space. However, this is actually a really nice final gut check before you delete everything.
Great product, works exactly as described for my situation.