yes it uses AR style mags (magpul pmags or lancer mags) you can add a foregrip as the OAL is 27.5 inches "unless your AR pistol has an OAL greater than 26 inches then you should not add a vertical fore-grip unless you first submit a Form 1 and get it approved." Specifications and features:
Kel-Tec RDB Semi Auto Rifle RDBBLK
5.56 NATO (Accepts .223 Remington)
17.3" Barrel
Twist Rate 1:7"
20 Round Magazine
AR-15 Compatible Magazine
Trigger Pull 4.5-5.5lbs
Bullpup Design
Ambidextrous Controls
Sling Points
Reversible, Non-Reciprocating Side Folding Operating Handle
Short Throw 35 degree Safety Selector
Reinforced Steel Top Cover
Ambidextrous Bolt Release
Synthetic Stock
Overall Weight Unloaded 6.7lbs
Overall Length 27.3"
Black Finish

Any AR magazines will work. If you have an AR-Pistol with an overall length of 26" or under, then you can't add a foregrip. However, if your pistol is greater than 26", you can add a foregrip because it's then considered a "firearm". Interesting.