The Apple branding App Store guidelines say:
"Always use the correct Apple product names with the correct capitalization as shown on the Apple Trademark List. Always use Apple product names in singular form. Modifiers such as model, device, or collection can be plural or possessive. Never typeset Apple product names using all uppercase letters."
("MacBook Pro" is one of the trademarks in the trademark l... oops, my apologies, Trademark List.)
So I suppose the correct plural is probably "MacBook Pro devices", but Apple's branding department has no power over us as individuals posting here so we can say what we like.
(I personally always went for "Macbook Pros")