Check valves/flashback arrestors are directional and designed so gas flows in only one direction and can not flow the other way. That is their purpose. A regulator flashback arrestor has a female fitting towards the regular and male threads towards the hose. A torch handle flashback arrestor has reverse fittings. Their fittings are male towards the hose and female towards to torch handle. It makes no sense to put a regulator arrestor on a torch handle because you would have to put adaptor fittings on each end to make that work.
My recommendation is to keep the check valves at the torch handle and put a flashback arrestor on the regulator on the propane tank. While very unlikely it is possible that your flame can cut the hose and the resulting fire find its way toward your propane tank making it a bomb. You don't need a flashback arrestor on the oxygen concentrator
5L oxygen concentrators have enough output for most tips. They can run rosebuds but not at full force.