The problem with rechargeable batteries is they are always lower capacity and usually have different voltage ranges. Capacity matters a great deal for high draw items like a flash. Voltage range tolerance depends on the specific equipment (manufacturers never specify). 900mAh seems to be the highest a rechargeable can get compared to the standard 1500mAh. That right there is worth a comparison during a long photo shoot.

Many rechargeable CR123As peak off the charger at over 4V. That could be a problem. While other batteries may not specify their peak voltage range, certainly a 3.6V battery will peak higher when fully charged. With some looking I've found 2 notable contenders, both of them boldly stating their safe voltage:

• a 3.0V with 3.2V peak at 900mAh (Tenergy) *winner
• a 3.15V - 3.25V ?mAh (Delkin)

I can't find capacity mentioned for the Delkin and it's more expensive so Tenergy is the winner. Note: there are two different Tenergy CR123A rechargeable batteries. One is lower capacity at 750mAh with a 3.2V nominal peaking at 3.9V. Avoid that one.

Last note: the linked site sells single batteries but also has a 4 pack, with charger and free shipping for $19 right now. Best choice and best deal.