I had one for my Game Gear that added more than few inches to the handheld’s depth, but did a decent job of semi-rectilinearly magnifying the screen. The backlight probably helped, since it wasn’t relying on light bounding in through the lens and then back out.
You’re more likely to inadvertently press obliquely just a little too much and have the whole thing fall over, spilling hot coffee and grounds all around while possibly breaking the mug you were pressing into.