Most people here would guess that my automatic response would be to keep them sealed (being a primarily MISB collector), but in the case of MP toys I have made somewhat of an exception.

The only ones I have MISB are 20th anniversary Prime and Skywarp. Grimlock I opened mainly because he looks better in bot mode and it was a space decision as well; MP Megs and Ultra Magnus I opened because Takara neglected to add a window to their boxes

In summary and to hopefully give you some guidance, my decision to open some of my MP toys was based on display value and / or whether or not I had the space. Just make sure you're comfortable with the decision you make because once you break that seal, there's no going back