Crushbup,
Your right, without loss of functionality you can get a .223 down to less than 160 db, especially in an open or outdoor setting.
However, with that said ... what is the objective of the buyer, they did not state it. Are they looking to protect their hearing, or to "stealth" their rifle?
If it's hearing protection you can get top of the line equipment for less than the typical cost of a suppressor and tax stamp ... and you do not have the local and federal boys and girls to contend with.
If "stealth" is the objective ... having the can, even outdoors, will produce noise levels in the neighborhood of that created by fire alarms, backup alarms on truck and const. eq., etc. Consider the "noise" created (100 db +/-) by the alarms mentioned ... do you want to lay out all that money, etc., to still have a report level that high. If the answer is yes, then heck, by all means go spend the money and enjoy your purchase.
If the answer to the above is no, and what you would like to do is shoot on your or another's property without drawing the ire of the neighbors (and possibly the "authorities") then move down to pistol caliber or even rimfire.