What is the difference between 74HC595N and 74HC595B1R shift registers?
It's a matter of manufacturer and specifications. The B1R suffix identifies a part made by STMicroelectronics, while an N suffix suggests a number of different possible manufacturers. The STM part is significantly slower than other makers' versions (55 MHz typ @ 5V for STM, 91 MHz typ @ 4.5V for SGThompson, for instance). At a guess, the STM part has a significantly smaller die than others, which limits the output drive into real loads, and produces a slower unit. But the smaller die allows lower cost.