I'm with you as far as using Medoc as long as I could. I did until I wanted to use features of GX Developer such as in-line compares.
As far as the FX0N and the A series communications, I am less surprised than your Mitsubishi distributor.
Use the FX configuration for the FX0N (understanding that you can't use all the functions that are available in the FX).
The A series may or may not be able to be programmed with Medoc (if your version of Medoc supports the A series) depending on the specific series and age of the PLC. In fact, some of the older A1S units resist communications with GX Developer. I ran into this once and had to find an old copy of Medoc to make modifications. One of the difficulties that you could have is the A1S may have difficulty connecting with a standard SC-09 cable.
Years ago Mitsubishi was having trouble getting enough power out the programming port for communications with the standard cable so they came up with a new one (cable) with a 5V power supply. Using an SC-09 cable, I found that the connection was iffy at best and when I finally hooked up, I made my programming revisions as quickly as I could. I own a powered cable but I was too far from my facility to get it. When leaving for the project site, I assumed the standard cable that I was using would work.
... rab