Some are just the same as the retail models but they are made lighter so that more customization is possible. Others are discontinued retail models. They typically come as a long hairpin so different lengths are possible from retail. They can also have different drill patterns (so different string patterns) compared to retail.
You can learn a lot more and buy them at the string forums.
4 x IG Prestige MP, 70 cm, 376 grams, 386 SW, ALU Power @50