QFT - Safety has to be priority number one!
Safety cables are a must too but even then the venue may not let you clamp to their balcony rail or over people's heads.
Good shock mounts are important, people sometimes pound on the balcony rails or bump into them etc. Without proper shock mounts the thumps would be transferred right into the mic's.
This. Don't even think about clamping and hanging your rig off a balcony, and over people's heads, unless you do it right and also use safety cables. Make sure every piece of your mounting gear is somehow attached to the cables. Bad enough if one of your microphones takes a dive, but hitting an attendee down below with a piece of your falling rig is unacceptable. Not only is it bad juju to injure someone but you'll put the venue in a position where they're liable and they could very easily pull the plug on open recording. Happened at a few venues I regularly taped in, thank goodness nobody got hit by the mics/gear.
I would suggest the articulated arms and/or extension poles due to rigidity as opposed to goosenecks, but that's a personal opinion.
And DigiGal's suggestion of shockmounts is a must. Unlike rolling from a stand where the stand itself can absorb vibration, you really don't have such a buffer when clamping. All it takes is a single ADHD case hammering away on the railing all night to make your perfect recording painful to listen to.