My friend gave me some advice, any good?

Bad... Mongoose has never beena good bike brand and if you found one for 800 bucks, it's made out of gold. We the people are pretty good but arnt the best, especially for street. If your looking for street bikes i would suggest: Stolon, Sunday, and fit, but deffinitly NOT Haro. Haro is crap now. If your looking for a race bike i would suggest: RedLine, Crupi, and Intense. And if you have the money... Definitly a Supercross, which are the best racing bmx bikes hands down but you can expect to pay a little more. Hope i helped