Nokia bh505 build quality is average, means the outer body. There are chances that it might get break, if you don't take care of it properly. but its not the same case with Plantronics BB 903+
Both of them can withstand water splash & they are sweat resistance.
the only plus point i find in Plantronics is the Voice Navigate feature. I mean when you hit previous button, it will play the previous track as well as inform you over speakers that "Previous track Selected"
Nokia bh505 comes with 3 different size of ear buds, while plantronics with only one. thats why its not confortable to wear for longer time & bass is not audible also. You will suffer once you lose the ear buds in plantronics.
Pricings point of view, Nokia bh505 - 2.7k, plantronics 3.3k.
Suggestion: I know, you love to ride bikes. You must wear helmet also, so in that case forget getting bh505 & plantronics bb 903+.
Get bluetooth Dog Tag ear piece from Jabra.
Otherwise nokia bh505 is a gr8 device.
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