they are very expensive to buy, and you'll only really need them if you're a real monkey with fixing things. i've tried with and without the jigs, and as long as you re-insert the head back in somewhere close, adjusting it into calibration is easier done without the jig. this is becasue the jig adjustments are very coarse and you can spend hours turn one way, then coming back and then back again.

just ensure that you mark the head you're taking out and put the new head back in close, and then just gently alter the position bit by bit. it will still take 10-20mins, but better than chasing your tail with the jig.

one word of warning: never remove all the heads together, as you'll be stuffed. always leave the black head in as this is the "master" head used for calibration alignment. if you need to replace the black, then fine, but do it individually.