Quite often, a single speedlight just isn't enough. You need more! You might need a smaller aperture than the single speedlight would provide (even at full power), or you might be battling very bright ambient light. High-Speed Flash Sync doesn't help you in that case. Then you need to add another speedlight.
The mount / bracket that I settled on is the RPS Light Bar with Four Accessory Shoes RS-3102 (affiliate). It is a bit unwieldy, especially when you have 4 speedlights mounted. But when you need it, you need it. It is this Read more inside...