I only heard about this pretty recently, and I've been using it for a week or two now. I'm pretty pleased with it, but I noticed that if you click the link to go watch the video on YouTube instead of the embed, timestamps get completely erased. Same thing happens when you click the YouTube logo on embed, but I don't know it that's intentional since it let's you keep watching from where you left off. Nevertheless, losing the timestamp by clicking the written link still sucks because you might not have even opened the embed when you do that.
Using the Chrome extension, btw.