Hi! Getting ready for the summer!

Should I buy a bluetooth-enabled MP3 player which is:

1. built-in to sunglasses (ie, it's fixed; I buy the player and sunglasses 
as one item)

or

2. attached to sunglasses (ie, it's removable; I buy the player and 
sunglasses as separate items)

Pros and cons welcomed; is there a 'killer' factor which determines the 
better choice?

Thanks and regards to Group.