They claim a typical accuracy of 10 square feet (< 1 square meter) which would be really really good.
Even systems with beacons are not better.
It really depends on how many routers are in your area. For places in cities, there are tons and tons of routers so its very easy to get pretty good resolution. For places more remote, you might not see many routers and then you would be for more limited in your resolution.
I'm looking at this for gaming applications. Don't need milimeter accuracy but +- 30cm would be good.