I've been using IEMs in rock bands since the late 90's. I've had my current buds for 3 years, Westone 3-driver. I forget the model number. I had the molds done by an audiologist tech and then sent in. If you sing harmonies, there's nothing better to hear yourself then with IEMs, especially with today's mixers that allow wireless on-the-fly monitor mixing from your iPad/iPhone. But for hearing your amp's tone, you have to spend the time with mic choice & placement just like you would in a studio. The buds will only reproduce what the mic signal is.
As for transmitters/receivers, you pretty much get what you pay for. The early Shure 400 system I had would always drop the signal out at the worst time, right in the middle of a vocal or guitar solo. I have a Sennheiser unit now and haven't had a single drop out. In one small club a few years ago, we ran with the buds directly wired to a multi-channel headphone amp because the stage was so small.