I'm skeptical on the internal one. We've all seen threads that are pushed out of alignment. The internal one only has one point so that point will just follow along the pushed over threads and not straighten them. You need several points that are still tracking in the good thread area so the first point to contact the pushed over threads will be held in position and straighten the pushed threads With only one point it will just follow along the easiest track. Stick to proper taps for that job.
I can't get the videos in the other sections to play but the external units look like many others out there like my mac tc-50 unit but they only have 2 teeth and not a small die with multiple teeth like the mac, hazet, snap-on versions which I've seen knock offs of on amazon for $70 - $80. I bought this one for axle spindle threads and other large threads where the cost of dies or machining was prohibitive. If this doesn't work out come the files.
