These devices allow you to load a program into an AVR that has a bootloader program burned into it, like an
Arduino or Arduino clone. Bootloaders are faster than ArduinoISP knock-offs, but slower than the serial and
parallel port programmers.
These are USB to TTL converter breakout boards that are intended to be integrated into your project
and dedicated to that use. They are not cheap, but are cheaper than the cables, generally, and make
for a nicely finished product.
These are USB to TTL converter cables that are intended to be used for all of your projects,
and not dedicated to a single project. They are a little more expensive initially, but you only
need one, where you might need one per project if you used breakout boards.