If you are unlikely to be using the saw regularly – I’d buy something like this which is perfectly adequate for cutting skirting boards.
https://www.toolstation.com/shop/Hand+Tools/d10/Saws/sd70/Precision+Mitre+Saw/p76675
I have one, and occasionally press it into service when I want a precise square cut; otherwise it sits rusting somewhere in the garage.
In use it needs fixing to a surface – the peg holes on my workbench are located just right to hold it securely.
A dual bevel mitre saw can cut two angles at a time. Imagine that you are cutting off a piece of wood with a 45 degree cut in the horizontal plane, at the same time the dual bevel saw can cut this at an angle other than 90 degrees through the vertical plane.
I’ve never had need to make such a cut, but then I’ve only used my mitre saw for skirting boards and such like.
One advantage of not having to turn a piece over (to make a cut), is that you are using your primary marking to position the blade cut – whereas with the piece turned over, your secondary cut marking might not be as precise (based on my own experience).