Well, I've tried out 3 different kinds of ear monitors in the last month.
First, I purchased a system manufactured and distributed by a company caled DB Technologies. It was inexpensive, I took it on trial, and then made my purchase. The in-ears were Sony buds, similar to a walkman type; round and they just sit in the outer ear. The major flaw was that they do no really block out any stage sound, so they have to be turned up quite lot to be heard. I took them to an audiologist to have them set into a custom mould and discovered it couldn't be done.
Next I purchased an inexpensive pair of Koss foam earpieces. The quality of sound wasn't very good.
Lastly, I tried out a pair of FutureSonic foam earpieces. Absolutely great drivers, clean sound, and the foam cuts out alot of the stage sound; so much so that I had to have the other band instruments put into my mix to hear them.
Now here's the problem. As many of you know, when you block the ears and play saxophone, you can hear the sound of the sax rattling around in your head cavity. It's much louder than a vocal sound. I found that I had to turn up the in-ears considerably to overcome that in-head sound. It had been my hope that I could listen to the in-ear monitor mix at a very low volume, thereby reducing the chance of further hearing damage, etc. If I was a guitarist, keyboardist, bass player, drummer, I would be able to run the in ear volume much quieter than for saxophone.
In conclusion, the in-ears are alot better than stage monitors, the volume is considerably reduced, but maybe not as much as your expectations might be.