Having read through the selection of 'news and reports' on the nobcprorep website, there are a few claims that lack support: one is that proportional representation will lead to a string of minority governments along with economic instability. I also just skimmed through the World Economic Forum: Global Competitiveness Report for 2017-2018.
Of the top 15 countries listed on page ix of this report, 8 use some form of Proportional Representation. One could fairly state that the majority of the most competitive economies operate with Proportional Representation.
Further to coalition governments, Douglas Todd's March 14th article in the Vancouver Sun offered a graph that showed a shift away from single-party governments to coalition governments.
If you look at the list, many are included with the most competitive economies.
There is a definite conflict between claims made by the "no" group and the available data. I'm inclined to go with the available data.