John, RDO is short for red dot optics meaning the slides cut to accept a red dot. The G in GR means it's the decocker only model. The R in GR means it has an accessories rail to attach accessories like a flashlight or laser. So if you want the decocker only that's the model you'd want. Hope this helps.

Hi John and welcome to the Buds Community. RDO = Red Dot Optics ready (meaning the slide is precut for the addition of a Red Dot). The G is the Decocker Only Model and the R = Railed (Accessory Railed). This is the Decocker Only Model : budsgunshop.com/product_info.php/products_id/139786/beretta+usa+92x+rdo+compact+9mm+4.25+13+1+gr+decocker+only+red+dot+optics+ready+black+bruniton+steel+slide -- Cheers and stay safe

Hi John, RDO means Red Dot Optics ready. G is decocker model only, F is safety / decocker. R stands for railed dust cover, so it has a pic rail for light or laser.
Stay safe & have a great day!