@RMK305
Does the Aten VS291 havve it's own external power supply?
Yes, it is an electronic switch.
I have also been looking at the VS201 which seems to be an automatic switcher.
I originally intended to buy this one because I wanted automatic switching too but I ended up selecting the VS291 on price. It was less than half the price of the VS201 and I thought I would give it a try. So far I am happy with it.
The VS201 also has a priority switch to select the primary input so that may help when the Amiga opens both a native and a RTG screen at the same time. The way I read their manual, the VS-201 would automatically select the primary input if a signal is present there.