While everything Blooie says is correct. However, there is a better reason to not buy bling for guineas.
I own guineas, lots of guineas. Too many guineas. I know them well. They are the bane of us responsible poultry owners.
If you buy them bling, they will not appreciate it. They will tell you they have lost it, or it fell off and they don't know where.
In actuality they will sell the bling to buy heron, meth or weapons. They cannot be trusted. They will use the bling to show their position in their guinea gangs. The tougher gang members will steal the bling from the younger ones.
So in addition to the reasons Blooie gave you. Please keep my reasons in mind,
Remember I have owed guineas for years. They are not sweet like chickens od kittens.... They are more like feral wild cats that just want handouts.