I use "+" in my Products Model on most of my products:
Example: Products Model = GFPM+9:
ZC : Widget 1 - (GFPM+9)
Paypal Express drops the "+" in processing/emails to customer:
PE: Widget 1 - Item#: GFPM 9
My issue with this is I have other products with the same model #, but no "+" so this is confusing to the customer and to me.
ZC: Widget 2 - (GFPM9)
PE: Widget 2 - Item#: GFPM9