I know that they recently raised some capital to invest in increasing sales. However I think a large proportion of their target market are grid scale and remote outposts for telecommunications/industrial applications.
That could be because their residential solution still cant beat something like the Tesla powerwall on price. However, I believe when investing in something that you expect to have longevity in the 20-30 years range it's better to go with something a little more pricey that is proven to last that long without degrading of performance, so on that point the flow battery wins.
It's like with solar panels, you can pay a premium upfront and get panels that will be producing the same output in ten years time like my parents did, or skimp on price and end up with a 30-40% reduction over the same time period like their neighbour.
I head about them several years ago but haven't seen much since. Do they have the scale/ pricing to sell to the average consumer yet?