Check out my post in this subject on the Radikal SAX 2:
http://www.sksboards.com/smf/index.php?topic=151388.0They are hit and miss as far as quality control. It's likely from the same factory, it just gets branded Charles Daly, Panzer, SDS and so on.
Be sure to clean the grease from the ARGO system, it's supposed to be clean and dry in the gas/piston area, but some lube where the rods connect with the bolt carrier. Also check the bolt carrier for peening where the rods hit it after breaking it in with some full power loads. The main issues I've seen are from people either running them straight out of the box and gumming up the grease in the ARGO system, or the factory failing to heat treat the bolt carrier, resulting in peening that eventually widens it out enough to lock up in the receiver.
The best route to add mag capacity is to replace the mag tube entirely, rather than use the two-round extension. I found this thread to be very helpful:
https://www.ar15.com/forums/Armory/Benelli-M4-Clones--Any-Comparisons-or-Reviews/1-520113/?page=35Every company has come out with some lemons, but I got a good one. I've got at least 300 shells through mine with 0 malfunctions. Mine cycles 3" magnums and WalMart bulk skeet shot equally well.
Be advised, changing mag capacity gets you into 922r territory. It's fairly easy with these from what I understand, with a new mag and follower, you will just need one or two more parts. That thread on ar15.com is your friend when trying to figure out what works and what doesn't. Daves metal works has good tubes from all accounts, but that's moot if you already ordered the mag extension.
I hope you get a good one!