I recently bought one of these:
Yesterday I took it on a century with temperates from -6C(21f) to -2C(28f) and my water stayed lukewarm all day. I found it slightly too small to properly fit in my bottle cage but a little hockey tape fixed that. It also doesn't hold quite as much as normal water bottles. I could only fit one in my front cage but someone with a bigger frame should be able to fit two. All in all it's better than having your water freeze.