hi gauv, Im sure it will do a good job, we have a couple of cheap , small in volume rain jackets and they do the trick as you wish--and are great in being so physically small.
My wife bought a pair of cheap rain pants that are probably similar to silnylon, again they would be sweaty in warmer riding, but great and small for the use you mention-to stop getting really cold and wet.

Touring I do prefer having my rain pants, rain booties and helmet cover for heavy rain and or rain in cooler temps, because I really don't like being cold and wet, and I can live with carrying my rather light full rain setup, even if it does take up some space.

I figure we all have priorities, and for me carrying the stuff is a compromise thats okay for me. Both my rain jacket and pants are pretty lightweight (I have the numbers written on their tags, I weighed them but cant recall the weights right now) and my shoe rain booties and helmet cover again are quite light, so it's all the compromise I can live with and happy with them when the conditions make me really happy that I have them with me.