i run a ds1 (blackspire) with matching bash
the ring isnt big enough to make the chain go over the roller but its a failsafe i suppose, i use it beacuse it was impossible for my chain to stay on with my urban riding. had to cut it to fit my full sus but it was cheap (£12!). it also has the full plate at the back so the chain doesnt catch either side. it works!
before this i was using truvativ two roller thingy but that just wasnt doing it for me as the chain was still coming off!
i dont run a front mech and my chain device is closer to downhill oriented more so than anything else, so a downhill device should do it.
i dont know how people run single ring without a device!
mine is slightly different to the picture, its four bolt and bb mounted with an iscg to bb adapter, also have a different bash
my bike with it mounted is in my signature