i have an xlab miniwing which mounts to the seatrails, it hold only two cages but has a spot for straps to carry a bag, and a slot for a nut that hold two 12g CO2 cartridges and a spare tube.
I eventually got the miniwing because i found it on sale for $30
The hydro tail only mounts to certain seatposts.
The minoura cages keep the bottles Real close to your butt.
And Xlab has a few different designs that all prevent bottle-launch, and i believe all mount to seat rails.