My Drift HD 1080 has a gap of about 4 seconds as it transitions between clips. Which in the Vlogging world can ruin an entire section of video if it switches at the wrong time! It's unlikely I know, but it has happened.
My Drift HD170 on the other hand is seamless.
But further to that, I have the HD and 2 HD170's hooked up to one remote. So when I push record, they all start together... sort of. The 2 HD170's start instantaneously while the HD kicks in about 4 seconds later! Very annoying! It's the same with stopping the recording.