Sodium batteries aren't exactly commodified yet, LFE is readily available and not terribly expensive.

For the most part I don't actually need batteries that work in the freezing cold, so much as survive it unmaintained for months at a time. I had solar panel damage last winter that allowed one battery to discharge enough to freeze. That is fatal to a standard flooded lead-acid battery.

If my test battery survives this winter then I will consider using the same type to replace lead-acid ones as they age out.