The correct way to refer to the plural of "MacBook Pro" is MacBook Pros.
MacBook Pro is a noun (a proper noun to be exact) and in the English language, nouns are pluralized. For example:
- laptop ⇒ laptops
- iPad ⇒ iPads
- Mac Pro ⇒ Mac Pros
The easiest way to identify that it's a proper noun is that it's the marketing name of the product.
Adjectives, will generally precede a noun as they describe it. For example: general contractor, managed device, and associate developer are all examples of an adjective describing the following noun.
Where the confusion comes in when we refer to (the handful) of adjectives that antecede the noun like the all to familiar attorneys general, surgeons general or courts-martial. These adjectives are normally reserved for positions in government, nobility or the military.
These are called postpositive adjectives where the adjective follows the noun.
- surgeons general ⇒ multiple "general" surgeons
- accounts payable ⇒ multiple "payable" accounts
- sergeants major ⇒ multiple "major" sergeants
If (somehow) we were to apply this to tech, we would use something like the following:
"MacBook Pros managed" ⇒ multiple "managed" MacBook Pros; but that is what sounds weird.