Greetings pitquim, and welcome
The transparent plastic has taken over as it is now also used for the LED module on the 'Lite' models.
Victorinox has fixed the problem of the lens popping out the clear frame, and they are no longer using the plastic lens, but there are many forum members (myself included) that prefer the old grey model. Supporters of the new lens say they prefer the wider field of view and longer depth of field from the larger lens and lower magnification. But I tend to hold the lens up to my eye for use, so prefer the higher magnification, and there are other reasons I prefer the old Explorer, such as the longer Phillips and wider large blade tang.