Samsung dual SIM phones don't seem to work well with rSAP at all. Even the S4 mini duos doesn't work well with stock Samsung rSAP. If you need a dual SIM phone and want to use rSAP, look for a Chinese MediaTek device (MT6577, MT6582, MT6592, ...). Some support rSAP out of the box, others should work with my app.
checked both Samsung HK and UK website, only state native SAP supported w/o rSAP. But thru the threads in S5 forum, it seemed S5 is wiz native rSAP. So I was confused by the specs on official website. It only can be assumed that S5 is wiz rSAP/SAP out of the box.