Hi, this is meant as a sincere question... I'm just genuinely curious...
Did you even try googling "data doubler mac"? You'd get an answer to your question in the very first google result.
This is your first post, you created an account today. It took so much more effort to post this question on a forum than to do a google search that would have literally taken less than 10 seconds to have an answer.
Sorry, not trying to be rude or snarky, but it just doesn't make sense.
Or... do the people who make/sell these products post questions like this in order to increase product mentions/links on sites like these?