Been using the Topeak Explorer rack for a decade on my Cannondale F4 Mtb. I use a Topeak MTX bag and it's so secure and convenient, I can't fathom using any other type of system. The bag slides on and locks into place in three seconds. No need to fuss with bungees or straps. Takes two seconds to unlock and slide the bag back off the rack.

The bag rattles minimally on the rack, it never bothered me. If it did, I could resolve it with a couple small patches cut from an old inner tube, and use spray adhesive to stick them between where the bag and rack contact.

Unless you're invested in some really nice touring panniers already, I would not hesitate to go with the Topeak rack and bag combo.