Yes they aren't the greatest things to look at but they work very well. I have at least 4 of them on different vehicles and haven't had any fail. One is in my chopped 66 Chevy 1/2 ton w/440 and it's been there since 2000. They just work.
Flush it out with a couple boxes of baking soda afterwards to neutralize the drano.
If any freeze plugs are marginal they won't be after this. But you'll be amazed by what comes out!