I've used both and both work the same way. If the ATAS-100 is available at
a "really" good price, would ensure it operated OK

After your comments, today I have bought the used ATAS-100 and, before buying, I have tested it.

I tried all bands, including WARC, from 7 to 50 MHz.

It has a good SWR on all bands except 7 MHz, where the residual SWR is too high for the FT-100D to deliver full power. With the manual procedure, I could determine that the antenna shows a clear resonance point on 7MHz, but at that point the SWR is not low enough.

However I still have to optimize the ground system in my car, so I hope the situation will improve on 7.

Thanks and 73

Tony I0JX