I use them. They do work, but you have to constantly add new ones.
Personally I like the look of them. Alder cones will also help lower pH and are available on ebay as well.
i just got some, as im trying to create a blackwater effect in my tank, there are a lot of different opinions on how many you should use, the ones i brought said that you should use 1 per gallon, personally i think just use how many suit you! i've put a lot in my tank as well as some manzanita root wood to help stain the water and obviously because it looks nice and yes they will float for a bit but will become water logged and sink soon enough