Rosetta Stone is all about language immersion...and that's a great thing. It's how I feel you can really get a language to become a part of your everyday life. However, there is little to no cultural immersion, and without the cultural context a lot of the stuff you learn loses meaning...also the pictures are sometimes vague and you are not sure exactly what the words are relating to.
It depends on what you're trying to use the program for. As a general basis, it's average at best. I find it's flaws outweigh it's pluses. If you have a public library you can check to see if they have any to loan. (They might not have kiswahili but you can check out any of the languages) All the pictures they use are the same...it's only the text that changes.
(I apologize for all the horrible grammar/spelling mistakes...it's an ungodly hour here...-_-;)
Hope it helps! Good luck!