Omni-directional is a feedback nightmare. I could not use a Shure live with my speakers even on the floor! I suppose if you're technical enough to get the gain, etc correct, you might be OK, but it is not an easy task.
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Live: Korg PA4X/EV Everse 8s/Senn 935/K&M stand

Studio: Korg PA4X/Yamaha DGX670/Boss BR900CD/Tascam DP24SD/MTM Iloud/Sony C80/AGK 214/K&M stand