Thanks for the response John. Two new questions I thought of:
1- When I render using the Mainconcept AVC, it took 17 hours to render a 30 minute clip (over twice as long as Sony AVC). I need a faster computer asap. But besides that, the clip would not play properly afterwards, even on my computer. Why wouldn’t the resulting Mainconcept .mp4 file work better than the Sony .m2ts (which play fine), since the input files were Mainconcept .mp4?
2- Since my original files were recorded at 59.94fps, is there not some drawback to rendering them at 29.97fps?
These are both curiosities and not complaints. Thanks again for your advice.