A:Answer Dekay replied that it includes a Unifying dongle, and that is NOT correct! See my included picture (M355 dongle on left, actual Unifying dongle on right).
It comes with a Logitech nano-receiver that isn't compatible with the Unifying series. The mouse itself can be paired to a Unifying dongle, but Unifying devices cannot be paired to the included one. It seems odd, but I just bought one and was surprised that the included USB dongle was not recognized by the Unifying software, until I noticed the dongle itself does not have the Unifying symbol on it (the mouse does).
So I grabbed a Unifying dongle I have and tried to pair the mouse, and it worked. Now my keyboard and this mouse can be used together with just one dongle.
Do note that once you pair it with a Unifying dongle, the included one seems to be useless. Unpairing it from the Unifying dongle will not get it to re-pair with the included one, and I have not found any other way to do it. Probably not an issue for most people, but I thought I should mention it.
