Great and often works when others fail BUT:
1- after last update, converting the videos after downloading takes ages and it's apparently because of the watermark insert that wasn't in the previous version. I hate this for two reasons; having to have the watermark and worse is the huge delay in aggregating the videos after download. It's ridiculous to have to wait for hours till a 150 MB video is aggregated!!!
2- VDH used to allow to download using firefox download manager and this can be so handy sometimes especially when you need to pause and resume. It's sad that VDH has no such feature anymore nor has it the ability to pause and resume downloads itself.
Thus I would only use it as a last resort when no other add-on or way works.