That doesn't sound like a good deal to me. I use Simple Mobile which piggy backs on T-Mobile. They charge $50 a month you get unlimited talk, text and 2GB of internet.
And Straight talk is cheaper than Simple Mobile for all the same, but their unlimited is "unlimited web browsing" of which I've been barked at 3 times for not having anything more than the base Android OS checks (Weather, email etc) and casual web surfing. -- "My weakness is that I care too much"
Well if you use quite a bit more data than 2GB/4GB it might sound good, I use Solavei myself and I get 4GB of data which is enough for me, 2GB is not quite enough for my usage.
This plan is clearly for people who use a lot of data, for them it's worth it you can't get that much data at the speeds that t-mobile provides in areas that are well covered anywhere else.
Their 2GB plan is $60 and going directly through t-mobile generally gets you better support with a store for in person support and more roaming privileges. To many the extra you pay when going directly through the carrier is worth it.