I don't think that they're at all necessary. I've never used one, but that's because I don't see the point.
If you want a cross-under, get a cross-under. You can also put a standard throatlatch on your cross-under and remove the cross-under straps, attach the reins to your noseband and voila! Side-pull!
If you want a bitted bridle, use... a bridle...
Unless you're cranking down the noseband or over-tightening the throatlatch, I don't see how the horse is going to feel differently about the Micklem.
The only option on the Micklem that I see as being potentially beneficial is that you can attach the rings of your bit to your noseband to reduce pressure in the mouth. I have two trains of thought about this.
1. You could use either a bit with a noseband attached (properly known as a half-breed snaffle), or use a kineton noseband- both transfer bit pressure to the nose;
2. Don't pull so hard as to require bit pressure to be transferred to the nose!
Otherwise, I view this bridle as a waste of time. You can accomplish all it has to offer with traditional methods.
...you will be more disappointed by the things you didn’t do than by the ones you did do. ... Explore. Dream. Discover.”