Tourmaline cabochon setting, advice needed please?

[Rfisher]

Hello- I've enjoyed reading here for years, but never posted. I now have a project that I would like some help on. I've searched the forum, but couldn't find any clear guidance...maybe it's just preference?
Anyways, I am having a lariat style necklace make with a north/south marquise tourmaline set by the stone vendor.
The vendor advises a combination bezel prong setting with a closed back.
The bezel /prong combo I am fine with....I'm having 2nd thoughts about the closed back????
Any help, thoughts and input would be welcomed!!!
Thank you!

 

[chrono]

Did the bench explain his/her reasoning for a closed back?

 

[Rfisher]

No, just stated he'd never do it for a faceted stone.....
Metal is 18k yellow, and I asked if it would effect the color. I was told no.
Stone is a translucent paraiba. I'm doubting this.....I need to ask more questions.
Thanks for the input Chrono.