For the BTUs they put out they do a decent job, also came with a mounting bracket that bolted right on to our IC CE300. For little more effort to install, the 12 does put out three times the BTUs.
We have a bunch of the espars. They work for about a year before road salt and dirt plugs the internal screens or the fan motor bearings seize. For the short period of time they did work they worked great. If you live in the rust belt or run on dirt roads I would pass. Focus on clean heater cores,good pumping booster pumps and removing the restrictive drivers panel heater valves and there will be no need for additional heaters.