These have become useful, especially with aluminum iMacs made prior to 2012. When I had to pull the glass off these units for the first time, I wondered what Apple had in mind as a means of getting the glass off without cracking it. After asking around, I learned that Apple was recommending suction cups and sending kits with specialized suction cups around to authorized repair shops.
As odd as it may feel to use these, they work well. Sans suction cups, there's almost no way to evenly distribute the amount of force you use to pull the glass from the case, and the cups even it out to help avoid the horrible realization/cracking sound when you've cracked the glass or put pressure on the wrong area.
For $7 per unit at Home Depot, you can find a QEP cup that's a great suction plunger for handling large tile, glass, and computer glass components. Just place the suction cup on the glass, tilt the handle to adjust/activate the airflow, and carefully pull the glass components off as needed.
It's important to note that starting with the 2012 iMac, Apple attaches the front glass to the panel display with tape, so you can't simply stick a suction cup on the glass and lift it off. You need to use a tool to cut the tape, such as iFixit's $8 iMac Opening Tool before you can lift the glass off.
This is about the riskiest tool you can use to pull your Mac's components apart, but it could also allow you access to components you might not be able to get to with any other tool. In the case of the MacBook Pro, a heat gun can help you heat up the 3M double sided tape Apple chooses to hold its glass to the LCD with, softening the tape to the point that the LCD can be lifted with suction cups and cleanly removed from the casing.
Keep in mind that this takes a great deal of expertise and while the cool cats at Small Dog Electronics have a useful instructional video as to how to go about this, do not attempt this unless you have someone who's successfully completed this task on hand to refer to, lest you wind up with a shattered MacBook Pro glass screen and the hours-long task of scraping broken glass into a wastebasket. Still, in cases where you take your time, have an experienced person on hand to guide the process and continuously check your work, a successful heat gun operation can go smoothly and save a lot of time in the long run.
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