Ahh HogWash!! Any way you can, I say. I have known guys to cut and drill a conventional can opener to fit on a keychain. Known a guy who had a self piercing spout which was probably the offical way as it was provided by the oil manufacturer. I myself have allways been partial to the quick violent puncture of a leatherman stabbing 2 holes, one to pour and one to vent into the can.
This nonsence about one method over another better in preventing metal flakes is just that, nonsence. There is no way to prevent it from happening and if it was a big deal there would be a mandated procedure out there that would be well known world-wide. The best way to prevent engine contamination is to keep your cans covered at all times. I believe we enter far more contamination pouring out of a can that has a layer of dirt on top that has been sitting exposed to the elements for weeks on hand...
Maybe we need oil cans to evolve in the manner that beer cans did, hey we get all worked up about the oil can in the engine, what about eating a can of veggies. I would be more concerned about eating metal slivers than pouring them into a engine.