Sailing downwind really requires a preventer to stop the main from an unwanted gybe.
The mass of the sail and boom puts a lot of strain on the attachment points. I have rigged a Dyneema line under the boom that connects to a bungy near the goose neck. This line has some loops to which I can connect a heavy duty 4:1 tackle. I hook it up to the cleats in the middle of the boat. To avoid shock loads, I have rigged a rubber shock absorber. Also I have rigged a shock absorber on my mainsheet. Works really well.
The advantage of using the mid-cleat is that you also pull the boom downwards, thus controling the twist in the mainsail. By pulling it downwards, I can ease the mainsail more without touching the spreaders. Adds a fraction more speed to the boat.