RE: single vs. dual conversion receivers
Firstly, the FMA M5 is a dual-conversion receiver (and a very good one).
Secondly, the Bergs (and a growing number of other SC receivers) do use a microcontroller-based decoder to help reduce the effects of interference from varous sources.
This alone can not significantly mitigate the effects of signals which appear on the image frequency to which SC receivers are sensitive.
While the Berg (and some other SC) receivers are perfectly adequate in many situations, the rather small price/size/weight difference that exists between SC and DC receivers means there's little reason not to opt for the latter if you're flying in anything other than a very remote area with very few others sharing your airspace.
99% of the time, a SC receiver will be just fine. However, if you're worried about that 1%, a few dollars spent on a DC receiver might be a good investment.