Honestly, I don't know for a fact, but my guess is that the 500 is the "regular" Progress and the 570 is the Progress XL, or long handled, Progress. I have a Progress XL, but have never seen a numerical designation for either Progress. Confusion aside, though, a Progress--whether regular or long handled--is an excellent razor. -Vance
Pretty sure it's the same razor; The 570 just comes with a case, and the 500 does not. That said, I don't own one. From my brief googling, though, it looks like the same razor.
Yes, I did some further research and the #570 is, indeed, the regular Progress (#500) with plastic case. The Progress XL is model #510. I learn something new every day! -Vance
Looks to me the blade guards are different. The 500 has a wave ribbed nostalgic looking guard, where 570 has a tech savy straight grooved guard. I'm lookin to get a progress but don't know which one to choose.