You really do need the best brakes you can afford, even if its stock replacement stuff.
Considering the admission of what you are doing with the car, the LAST thing you can afford to have happen is to have the brakes NOT work, and well. I would not skimp on brakes just to make the car faster (financially, that is) . The inverse is true, actually--you MUST improve the brakes if you do things to make the car faster. That is easy to argue, but it is a rule I will always follow.
Anyway, I don't have any experience with the company you asked about, and I suspect that the rotors are what is called in the parts business "off-shore". They might work fine, but I won't trust my car to what I consider unknown parts. "Off-shore" can mean alot of things, and even the stock parts on the Impala SS and many OE cars can be confusing--rear calipers are Australian, and rotors are Canadian, for the most part. I have a Baer GT front system, with Australian calipers, and rotors made in Brazil--but these same parts come across the GM parts counter in GM boxes, so at LEAST the General has "approved" them.
You are looking at a company (the site you posted) that will send rotors to you in white cardboard boxes, all likely made somewhere in a Pacific Rim country outside the North American continent. I'm enough of a skeptic that I'll spend more for stuff I can know absolutely is properly engineered, with good metallurgy, and yes, usually made in North America.
I do not intend by this statement to indicate that I don't on occasion end up using parts from non-English speaking countries, and it is not a cultural bias I'm displaying, by any means, so I hope no one reading this takes it that way. It is pretty much unavoidable, in reality, and some things "imported" are very good products....Bilstein and Koni shocks, from Europe, Bridgestone RE730 tires, from Japan, etc. Still, be cautious with brake parts.
With all of that, I would use Raybestos or Autospecialty HD (AR 9501/AR9502) front rotors, though there are other choices, too.
Calipers for the front are avaialble new or reman. I'd suggest a good reman part--GM has them available (actually these are packeaged as ACDelco DuraStop)as P/N 18037479 and 18037480, loaded (with pads). These remanufactured calipers come from BPI (Brake Parts Inc, the parent of the Raybestos product line) I think. These calipers cost about $60 each from a Dal or Sam, and they do have a core charge. You may or may not want to use the pads that come with the calipers. I think the DuraStop stuff comes with a warranty that is better than what new parts have.
Rear calipers I would buy new from GM. They are very inexpensive, thanks to the strength of the US dollar against the Australian buck. The P/N's are 18021517 and 18021518, cost about $55 each, and have NO core charge. ACD reman rears, with pads, are about $95 each, plus a core charge, so I see NO bargain there.
In both the front and rear, you also want to check the caliper "floating" system--in front, if you get new or reman calipers, this should be taken care of, but if the front guide pins don't come with the calipers, you might get them too. Also, it would not hurt to have a GM 18005606 caliper service kit on hand, just in case. In the rear, its a little more complicated, with the anchor bracket, guide pins and seals all to be checked and if necessary, replaced, in addition to the caliper(s).
What about the flex hoses? How many miles on the car?
Brake pads: there are many choices, but Performance Friction has very good market coverage. There is also OE, ACDelco ceramic (which comes from BPI/Raybestos), Raybestos (many different friction compounds, and some are too aggressive), Wagner, Bendix, Hawk, and a ton of other lesser-name products. The one thing about the rear calipers is that the anti-rattle clips that come in the OE rear pad kit don't come in any of the other brake pad kits that are available, to my knowledge. As far as I know, Hawk still does not have a rear pad set for the Impala/9C1, FWIW.
If you are replacing the front rotors, you will be needing front hub inner seals, and you might as well use new wheel bearings, since the new rotors will have new bearing cups already installed.
Plan to completely flush the brake system, and use GOOD fluid.