I have stated this many times in other threads. Single driver buds are the most common reason (based on personal experience, forum posts, etc.) that folks don't like IEM's, especially guitar and bass players.
If you play bass/guitar and use IEM's, you NEED (at a minimum) dual drivers.. single drivers do not have the sound stage, definition or clarity one needs.
For some, universal fit works.. Custom fit (molds) are more expensive, but if you use IEM's, get A DECENT set of MULTI-DRIVER buds.
If not, it's like playing an $30,000 audiophile stereo system thru $10 speakers... you wouldn't do it for that system, why do it in your ears??