In my experience, the best way is the hardest way, one pore at a time with a narrow tipped soldering iron or wood burning kit. I would be concenernd that the Brownelll's punches will not make the pore deep enough absent some significant downforce which wold likely bring the rounded edges into play.
Be advised that the polymer of P-Mags, Glock Mags and the Glock pistol themselves all behave differently when given the heat. While practice on a non pistol item is helpful, there is no substitute for a gentle and patient touch. The first stick is the hardest.
Surface prep with a dremel is needed to go to the next level visually. A dremel can also take off too much material too qucikly both abrasively and via heat.
In a worse case scenerio, you will dremel right thru (or nearly so) the grip and ruin the frame.
Gun # 2 I stippled. Glock 35. Removed fingergroves, cut mag pull outs, misc frame touchpoints, very little surface prep.
Gun Number # 42 (approx). G 21SF. Removed all factory checkering and fingergrooves, 360 degree stippling. Signifacnt surface prep with dremel reducing/elimnating molded checkeing, mold lines etc.