188.8.131.52 was the first build released, I think, in November 2013. It could certainly open model files - but it's also certainly worth downloading the 12.4.2 release. From Datawatch's main website, there's a link to the support portal, from where you'll get the links to download the files you need.
So it didn't occur to me to try and open the model file another way I was using File Open, as in select any file. The dmod file extension will open if I go to File Open Model File, it is the same way with Project files created in v184.108.40.206. Is this a bug in the current version or something? I registered on the support site and am looking into upgrading as soon as possible, but until then just curious.
Monarch/Modeller has always expected a specific "Open Model" File open election since the ability to open a model without first opening a report or database was introduced.
You may be able to start Monarch/Modeler from a Windows based "Open File" if the file association exists - not sure and I'm not sure there would be a useful point to it (though there is for a Project obviously).
Some years back the models files had .mod extensions that also ended up being used by other software so "open with" was a little erratic at the time.
Just got done talking to support and upgraded to the new version, it has absolutely no problem opening my dmod files without having to go through File -> Open -> Open Model, now I can just click the folder icon to open it like a normal file and it loads perfectly, saves me valuable seconds . Thank you!