I've used liquid masks quite a bit, mostly the Winsor & Newton version.
Pros:
You can easily mask off nearly any shape you want.
Virtually zero problem with bleeding under edges.
The "Ta da!" moment when you peel off is a nice reward!
Cons:
Tricky to apply evenly, but if you don't disturb it even a very thin film will mask effectively.
Getting the edges neat can be a bit of a pig.
Expensive for large jobs.
Figuring out what makes a good application tool. No brush I've ever tried did the job worth a damn, I used to end up spreading it with the end of a bamboo skewer or cocktail stick half the time.
It is not easily peeled from anything it will absorb into.
Thick applications can be slow to fully dry but be patient. I used to spray right over the top of it once it had skinned over, but with brush application you don't want to disturb the skin and get liquid latex into the brush.