Some have tried it, but not me personally. I prefer to mix the coffee with a spoon of coffee and the same with the vanilla, just to give it that extra taste. Both with ice cold water.
I find them ok that way.
I've managed 4 weeks on them without a problem.
Just starting refeed today and gone for chocolate all the way with the shakes.
I mix half the chocolate with half the vanilla some days and I love it, makes it more like a creamier milker chocolate, its lovely. I have it warm before bedtime.
I must be one of the really, really lucky ones because I just LOVE all three shakes, wizzed with lots of ice. I haven't touched regular tea or coffee, just an occational peppermint tea as I always was a fan of plain water, hot or cold.