In the mobile version, it’s hard to watch a tag, as you can’t really hover a mouse over it. I can’t even hover my finger over the tag to cause a mouse over type thing to happen like with some sites for some reason. Instead I have to either press on the tag and press watch before the tag search loads, or hold the tag and make it highlight the text, which then counts as a mouse over.
I’ll suggest maybe having the + (or -) clickable to watch or unwatch a tag. Or perhaps have some other system of doing this exclusive to mobile, since the way it is, is completely fine for desktop.