Please refer to Colin Archer and Redningsselskapet.
The Hartley is a copy of Archer's most famous design, ferro cement, gaff rigg, full keel, usually home built. Thats not a great start. It is quite possible to build a good boat in ferro but they are as rare as hen's teeth. They are cheap to buy, largely uninsurable and as a result have bugger all resale value. Even really good ones, and they do exist, have ordinary resale value, worse even than steel.
However I guess you didn't ask for opinions on ferro as such so I'll stfu on that subect.
As for double enders ... refer K Aage Nielson, Bob Perry, Bill Crealock. When you consider the output from those guys then it is simply not possible to slam double enders per se. Reality is there are gooduns and baduns. Those three tended towards the goodun side of the equation and I for one would be quite content to go to sea in one of their double ended creations. Beautiful is a word that also comes to mind.
Of course around about now I'd be expected to get stuck into gaff rigs except that the Perry fellow just happens to have designed a couple that seem to work quite well, hell one of them is a schooner that from all appearances honks along quite nicely though he resisted the temptation to build her out of concrete.