I have used liqyid masking take quiet successful.
Found it most useful for masking recessed areas like eyes in 1/8 figures, canopies and they like.
If you got a good separation line like panels(Robots) or similar it also helps.
Here is how I use it:
1.) Apply to or 3 layers of the masking liquid(one does not guarantee good & even coverage)
2.) Trim any excess away that might have spread into the area to be painted.
3.) Paint the Model
4.) Take a SHARP knife and cut along the masked off area, if you don't do this there is a good change the the paint might peel of the unmasked area when trying to take the masking liquid off.
5.) Roll the edges of the masking liquid INWARDS and away from the painted area, keep doing this till you can take it off nicely and easily. DON'T try to peel/pull the stuff off
Of course I lay down a top-coat prior to using any form of masking medium.
You can use it, but it will give you a sharp outline similar to masking tape.