I grow Old Cape Roughskin and Eureka. Of them the roughskin is by far the better of the two - hundreds of fruit almost non-stop and a real lemon flavour - if they are left to ripen to just under orange they are sweet-sour with the most aromatic oil. Superb on anything (including lamb!). Bit of a bitch to harvest though with the thorns. And they grow true from seed.
Eureka is nice for market - it's a good looking lemon but not as juicy and the oil is more bitter and not as aromatic.
Besides the thorns makiing harvesting difficult I cannot fathom why the roughskin has gone out of favour. It is far superior to the modern cultivars that taste like citric acid and not much else.
Jim, I know that Bush is an Australian cultivar that can be a bit bitter - it might be a hybrid with a calomondin or citron hence the shrubbiness and bitterness. I know there is a very similar cultivar called Madeira Roughskin - it is pretty much the same thing as the Old Cape Roughskin from what I've seen. It is occasionally available in nurseries here - it is very popular with the Portuguese community that originated from Funchal Madeira.
The Cape Roughskin is a really old cultivar - we have numerous plants with the "Old Cape" or "Early Cape" prefix - mulberries, figs and roses amongst others. It dates to when ships from the east would dock in Cape Town (1600 -1700's) on their voyage back to Europe laden with trade goods and novelties. Because it is so well adapted to our climate it is used as a rootstock on most of the commercial citrus cultivars or those that would struggle here such as limes.
Luckily it is entrenched in our cuisine and is freely available from nurseries here. It is often grown as a security hedge - the thorns are about 2 inches long and very stout. Travellers in the 1600 & 1700's in the old Cape Colony would often remark that farms had hedges of them around the animal coralls to keep lions at bay!
The juice has a superior depth of flavour - and it produces lots! It is more spongy than the firm-fleshed modern cultivars.
They grow very easily from seed - I constantly remove seedlings from under the big tree (it produces more lemons than we can possibly use - and we drizzle lemon juice on almost everything).
I will gladly send seeds to anyone who's interested.