Ive heard real good things about diamond audio being really high quality gear and giving crystal clear sound output, they certainly look good quality.
The seller UltimaCarAudio is a good seller, i bought my polk momo 6.5" components from them which were a little more expensive at 179.99 a pair but they are the best speakers ive ever heard and factory standard in some ferrari's i believe so they would be a good choice also have a look at them.
But yeah the diamond audio stuff gets good ratings from what ive seen of it.