Not a fan of the ones that are attached/part of the gas block. There is a separate flip up iron sight that attaches to the barrel, however I haven't been able to find one. The RCMP C8IUR uses this type. But again I haven't found it for sale anywhere. Plus as already mentioned there is a height difference with the Stag 10 / DPMS AR308 rifles vs AR15.
The railed gas block idea is your best bet. I actually do have back up iron sights on an Armalite AR10t where the front sight is on the railed gas block. Sorry I don't have any current photos with backup sights on. But you can see the railed gas block with this photo. Edit: I've added some newer photos which do show the GG&G sights.
The backup sights that go with the Canadian forces AR10t are the GG&G ones. They are decent quality and look good on a more retro style AR10.