I have recently made this jig for my trim router based on a few YouTube posts I found. The large flat base and handles make the router easier to control, especially when doing edge round overs. Less chance of it tipping over edge. The extensions make it easy to cut dados/slots up to about 330mm from the edge.
I tried to get a spare base assembly from The Toolshed without any luck, so got one off AliExpress for $13 delivered. Looks like most of the trim routers of various brands are clones of each other, or just a similar size.