The latest alpha version should fix the problem of only having ADP variants available on youtube:
Video DownloadHelper 5.5.0a4It's working stably on my system and no one has reported any real issues with it so far.
Aggregation will be very slow (and suck up all your cpu usage) as you described if the converter needs to re-encode the video. The video may be re-encoded if:
1. You don't have a registered converter license (VDH inserts a watermark in this case which requires re-encoding the video.)
2. You have the option 'Force H264 tuning in aggregation' selected.
3. You have set conversion options that convert the video to another format.
As long as the converter doesn't need to re-encode the video the aggregation should only take a second or two.