Has anyone got any experience ? I saw this on AliExpress and thought it wasn't too bad a price ?
They do look like the way forward but not yet unfortunately.
I've not gone into them massively but it seems the big disadvantage with them is the discharge voltage which drops off quite badly and continuously as they discharge. So yes those cells may well give you 200A for an hour but a vast amount of that energy will be released at an unpractically low voltage, eg your inverter will soon go into low voltage cut off. Don't think they'll catch on until we see the introduction of power boosters that are able to give a constant 12V output from a wide voltage input range at high current, or a range of 'sodium compatible' electronics is introduced.
You could of course just use the 'top 1/3rd of the battery capacity but you'd then need 3 batteries to give the same capacity and spend 3 times as much money!