This group spams these letters out, I get them from time to time. It feels a bit scammy, but I can't say for certain that they are a scam. Probably just very aggressive marketing.
I have a 10kw battery, and unless you want to feel better than everyone else, I don't think it's worth it. With the battery you should expect your feed in rates to go to zero (increasing your bill), as you'll charge the battery during the day. If you can keep your usage under the battery capacity, your grid usage will be near zero. It's also potentially useful to be able to run your house on battery if you have a power outage, but that is an optional extra ($300).
I tried out Amber for Batteries, but it quickly became clear that there isn't really a way for it to be profitable. Usage is always ~20c higher than feed in, so you need to have a lot of battery capacity to ensure you don't run out and need to start pulling from the grid.
There really is no free lunch anymore, and solar and batteries don't strike me as being valuable investments anymore.