Back in the heyday of DEs the TTO replaced the 2 and 3 piece pretty much all across the board. At least with DEs in the USA. The ease of loading, particularly when Gillette supplied the blade dispensers that were made for that purpose, eliminated more handling of the naked blade, and more cut fingers. TTO is quicker and safer but the 2 and 3 piece DEs are cool too. A merkur slant is my favorite DE and I've got them in the 2 and the older 3 piece versions.