T-Rex Grille upgrade

[C-Dub'sZ71]

Im looking to change out my grille and have narrowed it down to the T-Rex stealth X-Metal series. My issue is they make two different styles, the overlay and the inserts. Their website is a little unclear as to the install for either of them. I know the difference between an overlay and an insert but there is a review on the overlay that states it is not in fact an overlay. I was hoping someone on here has done one of these swaps and has some insights. for anyone who has done a true swap how difficult was it and for anyone who has done an overlay can you see the preexisting grille behind the new overlay? TIA!!