This potion completely fails, you don't get the dispel, you don't get the other spells, the game spams you with 3 lines saying "You need to be able to speak to do that." or whatever the message is, I forgot to grab a screenshot of it, but just try using it while silenced and you'll see.
This potion when not silenced, applies the dispelmagic effect, but then fails to apply the reduce and bless effects afterward, saying "You're not ready to perform another action!"
This potion works fine.
This potion completely fails, you don't get the dispel, you don't get the other spells, the game spams you with 3 lines saying "You need to be able to speak to do that." or whatever the message is, I forgot to grab a screenshot of it, but just try using it while silenced and you'll see.