Don't know about your exact question, but we have brought 2 computer monitors in original packing and boxes as checked luggage recently. Flew MIA to PUJ if that matters. And did not have to pay a peso.
Two different trips; aduanas questioned us and opened the boxes. We just insisted they were not TVs, rather monitors, which was the truth!
We nearly had to pay for second one as they wanted to say it was "new" because we had in original packing. And it did look pretty new because it had only been purchased on that trip. But we convinced them otherwise. Somehow we explained that we use the original boxes to travel with the monitor; again true statement. We only speak a little Spanish and have Residentias, so no clue whether that is/was a factor.
That second one was actually a complete computer and we could have turned it on to show them it was already set up and had been used. But we didn't tell them that because they let us go before we had to go that far.
And we were definitely risking damage to them by checking with the airlines. But shipping we thought would be more risky. Both made it through just fine.
BTW, both were 27".