OKay, a few things to know., First, they are dangerous in the hands of inexperienced people. Second, do NOT run with only one ear... that is a good way to loose hearing in that ear. Third, they isolate you from the real world, so you will have no idea of what is really going on around you. It is really disconcerting and can be pretty fucked up. Fourth, in my opinion, if you think that you need in ear monitors at rehersal, you are rehearsing too damned loud.
Fifth, they are really cool, and a great way to keep control of things if you are a traveling band playing on unfamiliar stages with unknown PA systems. On the face of it, it can be expensive to set up a traveling rack to handle your in ears, but if you do, you'll always hear the same thing in your monitors all the time, and your shows can get a lot better and tighter and you'll sound better because you can dial in your mix.
But you may face all sorts of expenses related to this, depending upon what type of venues you play. In other words, if the system at Joes Bar has one monitor mix, and you need five, then you have to split all the mics and go to your own monitor mixer to get your mixes. So now you need a mic splitter and a monitor console.
For the average club band it is a long way to go and a rather large expense just to avoid learning how to control your individual playing volumes. But it has a place in the grand scheme of things.
Bill
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"Is it possible that he was alive when you began the autopsy?"
"No. His brain was sitting on my desk."
"But could he have been alive?"
"He could have been alive and practicing law somewhere."