I bought an "Apollo" clinch tool for about $30 at a big box store. The hard part is getting the tool into tight spots, especially hooking up tees at the back of a cabinet. Gotta think those thru before jumping in.
That fitting is a 1/2" swivel iron pipe adapter, only a few bucks to replace if you scratch it. Alternately you can use a "push connect" fitting to replace that swivel, no tool required. Look for "Shark Bite" fittings at any well stocked hardware store.
Yes, a 5/8" OD pex is the nominal 1/2" size pipe.