Yes, they are safe if done right but they are a PIA as well. They are brand and hose specific and you need special dies for them. What that means is that if you blow a hose and need one on a Saturday, you can't go to local farm supply and get one made. You have to go where they have the right press/dies for your couplings. My Cat has reusable fittings and someone before me had replaced a hose with a non Cat hose and put a piece of tin in as a spacer. It was the main hose from the pump to the loader valve. While using the backhoe, the fitting blew right off the hose dumping 15 gallons of oil on the ground. I had to lay in this oil to remove and replace the hose. The hose was still good with the rubber cover nicely removed exposing the steel braid. I put a standard hose and fittings on to fix it.
Cat has their own reusable fittings and advertised they were cheaper than getting a new hose with fittings made. That's not exactly correct. There are a lot more steps in removing reusable fittings and putting them on new hose than putting standard fittings on new hose, so it often costs more money. I've heard that Cat is doing away with their reusable fittings on newer machines.