Tried the Liquid GS, and it was ok. Pretty fiddly to get the hang of, but it definitely has its uses. Good for filling hairline cracks and things. Worked best when I brushed it on with an old ragged brush.
Then I tried the Vallejo Plastic Putty, and I found it much better. Similar product, but far easier to work with, dries harder, takes sanding better. Have to recommend it over the GS.