Quality foam, not quite a perfect fit for FiiO F9
I bought the Mercury 4.9mm to replace the stock tips. It wasn't listed as being compatible, but the measurements were about right--so I took a chance. They mostly work, except the left one usually gets left in my ear when I take them out. They do make these IEMs sound a whole lot better to me (good seal keeps the low and mids from leaking out).
Would recommend to a friend.