I have been researching this on amazon and other places- some of the more expensive ones say they have advanced features? what does that mean? what does a $400 one do that a $40 doesn’t? Unless i can hit a button the $400 one and it actually fixes the problem, otherwise, i can only imagine it has more codes for complex issues?
Probably the 40 one is just basic tool that can read basic engine fault codes. And maybe life data from engine control unit.
400 one can probably access more control units on most vehicles. Maybe it can also send some commands. For example to program in a new module, to bleed abs, to set rear brakes to maintenance mode to replace brake pads etc.
But there are also lot better and more expensive scan tools. They can access more of that stuff.