Should i get bass blockers?

I was reading a review on a pair of 4'' speakers i wanted to get in addition to other upgrades i'm making on my cars stereo system, and they recommended bass blockers. I was wondering if anyone could let me know if i'm gonna need them. I'm gonna buy the: JVC KD-HDR60 Receiver, 2 pairs of 6.5'' Pioneer TS-A1684R, and either the Alpine SPS-400 or Polk Audio db401. I was thinking that either of the 4'' speakers will be fine without the bass blockers cause the receiver goes to a max of 50 Watts and the speakers cruise at 45 watts RMS. Any opinions on the possible situation, or any ideas or recommendations on my future speaker setup.