1. It would be nice if there was a short video, gif, or webm showing TubePen working. I see the image examples and they are nice, but seeing it "in motion" would be a nice reassurance before signing up.

2. I use brave browser on mobile to watch youtube, so videos automatically set to m.youtube.com/whatever. In order for me to try TubePem on mobile I had to drop the leading "m" subdomain and switch youtube to TubePen. Not sure if you could get things working with the subdomain m.tubepen.com, but it might be nice.

Anyway, cool idea. I hope it does well. :)