They’re only worth considering if you feel you need to clear your colon after accumulating years/decades of crud, and that shouldn’t take more than 3-4 sessions. After that, I don’t see why you’d ever need another one if you’re taking care of your bowels.
You need to normalise and reinforce your gut flora to be healthy and overcome candida, and a colonic couldn’t be more disruptive. It won’t just clear out (some of) the candida, it’ll take along a lot of beneficial bacteria too.
You’ve done the cleansing, so now you need to start on the healing. Personally, I’d cancel the appointment and start focusing on the protocol.