I attach S hooks (see image) to hang my blocks from the boom. I find a smap shackle best on the travler. It is fast and easy to attach and remove.
I've had an S-Hook open up (ended up looking more like a J) in a big gust with a fat head main on the 6.0. I'm guessing depending on the size of the main you might be fine with one, I don't trust them for that anymore.
