I've never heard of these, but I'll keep a look out for them. Wasn't someone on here saying that beer has been getting progressively stronger since the early 20th century? In which case these beers might be like what people were drinking back in the 18th century!
Beer strength was declining at the start of the century, & dropped dramatically (due to government restrictions & shortages of materials) during WW1. It never regained its pre-war strength, & in WW2 the government required it to be weakened again.
It's been gradually getting stronger since the mid-20th century.
Average specific gravity, UK:
1900: 1055
1910: 1053
1919: 1031
1927: 1043
I'm pretty sure we're not up to an average of 5.5% ABV (rough equivalent of 1055 specific gravity) yet.
In the 18th century, there was a distinction between small beer (mentioned by some here already), which was weak, & drunk for refreshment, & stronger beers.