My reason for OTG is that I'm using an android phone and live in europe. If you want to keep legal and use CE mode you have a pity range. Second problem is that androids can't use 5,8ghz. So normally the only way is to use 2,4 ghz for phone and 5,8ghz for drone connection. But 5,8ghz + CE mode = range under 100m.
With otg cabel I can use 2,4 ghz for the spark and get a range around 400m.