Yea your are right . But if your a southpaw then a impact is not going any use for you . However if FX would reconsidering in making the impact so we the southpaws can use it like the DDW then I just might reconsider getting the DDW . But we all know that will be a cold in hell for that happens .
I am a Lefty and i had the same reservations about the Impact until i spoke with Ken, he assured me that he had sold many of them to left hand shooters and none of them reported any issue.
Long story short i had him set me up a Compact MKII in .22 and i can tell you with Absolute certainty it is Not a problem shooting an Impact as a lefty..
Now full disclosure i did go ahead and order one of the Ambidextrous Cheek rests from the dude over in the UK on ebay, but even without it i still had zero issues , the new rest is more comfortable since it is rounded on both sides..
The 28 round mag is not an issue , it sits far enough back to not be ..
I am a Big dude , 6.3" tall , 255lbs and Gorilla hands and the compact feels Very good to me..
Bottom line do Not let being a southpaw influence your decision ..