I did a bit of a deep dive into this.
It looks like a potential workable option for utility scale storage but the 20 yrs use case with no degradation is a bit of a stretch.
As far as I can tell the major downsides are that these batteries are large. 200kw is the size of two large shipping containers. Compare that to the 100 kw in a model S.
The other major downside is that they require maintenance unlike the Li cell option. Because the electolite is either a strong alkali or a strong acid that is pumped round a circuit. Pumps and seals can fail and need to be replaced by a trained individual wearing not insignificant PPE. There are about 2 pumps per 100kw so for a 100mw installation (the size of the utility battery Tesla installed in Australia) that’s about 2000 pumps and many more seals / connections.
When a cell fails. You need a forklift to remove it.
So if you install one of these batteries at utility scale. You will need a huge area and a team of engineers and parts to maintain the battery for the 20 yrs life span.
So if you plug it in it’s unlikely to be working 2 yrs later without significant maintenance.
As far as I’m aware the Tesla utility option is plug and play and maintenance free for 10 yrs then individual units can be replaced. Each unit is made up of 1000’s of individual batteries not unlike AA’s. Each cell is fused so that if a cell fails it is automatically isolated from the stack which accounts for part of the battery degradation over time. Hence it is auto maintained.
The flow batteries appear to solve some problems that the Li solution has but at the same time creating greater problems elsewhere.
Despite having a 10yr life span, the Tesla type Li solution is probably cheaper, more convenient and takes up a fraction of the area required by the Flow batteries over a 20 year life cycle.
Hat tip to @Slasher
See this company offering commercial utility scale Vanadium flow batteries viznenergy.com