Gillette invented the safety razor about 120 years ago, even though they lost interest in it when they discovered they could lock buyers into buying very expensive plastic cartridge razor blades. This happened because everyone started to manufacture standardised double edge blades that could fit any other safety razor, and profits on blades were very slim.
But safety razors and blades are going stronger than ever today as many shavers have rediscovered them to be more environmentally friendly, better for the skin, and way cheaper to use.
Competition means cheaper prices, but also a mass of options to choose from. There are many brands of blades that offer a different shaving experience (with the same razor) due to different sharpness, shaving angle, smoothness, etc. So although you buy one razor, test out a few different blades with it, as the experience will be different with each blade brand.
Gillette is not "the best" safety razor out there, as there are many excellent quality choices to choose from today. So spend some time watching reviews to get an idea before choosing. Although a razor will last a few lifetimes, many shavers do end up buying a few more razors to just try out different experiences. I've even bought an Ikon handle to replace the handle on my Edwin Jagger DE89 head.