The short answer is that if you received the update to 2.1, you've already got .3P. Otherwise, you've probably got .2P
Advantages are somewhat sketchy, but I can say that in local known poor reception areas (ie, no signal at all with my old LG enV3, which is regarded as generally having good reception), I can still get 1x with at least one bar on my Droid. I also seem to get 3x pretty much everywhere...except in the basement level of the local mega-mall (where I get no signal).
I don't see a downside, personally.