People used to resharpen safety razor blades. Not worth their time. DE razors are fine as long as the blade is sharp, but you have to change it 50-100 times per year, and there's a decent chance of cutting yourself.

At least on the first few shaves, the three bladed ones have a lot of research behind them, and are technically superior to the single bladed ones; there's a lab in long island that pays men to test razors that has evaluated this.

Whether the increase in quality and reduced effort is worth it is a personal preference