I use pendulums to choose a deck when the sitter or I, can't decide on a deck! I ask what is the best deck for this reading? Works so well for that!
I also have used pendulums to check a reading, have I got this right? it's never let me down for that either and useful if you are sending the reading to someone. I have more confidence in myself these days though with that.
But it's important to remember that we can only get a few answers from a pendulum, it's practically binary in response. Tarot works differently in that it can give us such insight! I think it's important to remember the limitations of the pendulum. Tarot is not binary in the same way.
Even doing a spread with two options, it will give you more than just "this is the right decision". That is why tarot doesn't work so well with Yes or No questions, it's limiting. But the pendulum is wonderful for that. I would use it to ask which option A or B is the best? but use it in conjunction with the big picture from the tarot reading. There is no problem with dowsing with it though, give it a go and experiment! Mixing systems is fun!