[akashakya]

With multiple cursors you are seeing the changes as you are editing. and you have all of the normal editing shortcuts at your disposal. Example, if you made a mistake while typing just hit undo.

[bhaak]

I would rather add the c option in cases where I'm not 100% sure what I'm doing.

So in this case :'<,'>s/_b/B/c

That let's you step through every change and if something's wrong you can press ESC and u to undo only the last change.

It depends on the actual problem of course, but multicursor edits also get unwieldy if you're editing more than 2 or 3 lines.

What about if the lines are beyond the visible screen?

[akashakya]

Yes, no silver bullet. But most of my use case I find a generic pattern so I don't check the individual edits. Anything more complex I'll switch to macros.

Btw, I meant undo like global undo which will let you undo the last keypress for all of the cursors. In your case, you meant undo for a particular instance of change I guess.

Also, let's say there is different character after _

  foo_bar -> fooBar
  baz_car -> bazCar
  some_thing -> someThing 

Maybe you can do this with regex. but for a new user, he has to look it up. With multiple-cursors, you don't even have to think about it.

However, you can use a macro.