Firstly, congrats on your twins!
Secondly, I also had not heard that Aldi did a baby formula.
I have always used S26-Gold with both babies and have not found it to be too expensive (Big W always has it cheaper than the supermarkets, and sometimes have really good specials so I would buy 8 tins or so when that happened!)
There are very strict controls on the standard of formula, and so for it to be on the market, it must be of a certain quality. It may be that another company is making it for Aldi and re-branding it.
Also, you might just want to see how many actual scoops you get for your money, if you need more scoops per mL (40, 50 or 60mL per scoop) IYKWIM then you might be better off with another brand.
Another reason that formulas such as SMA can be cheaper is that they are made with casein, instead of whey. So maybe check the Mamia tin to see if it says Casein-dominant or Whey-dominant. Not that there is anything wrong with it, but SMA was recommended to me to use overnight with my DS when he was getting hungry a lot - it apparently makes them fuller for longer. I did not really find this to be the case to be honest.
Also, I believe that for a formula to be called "gold" it is because it is containing extra omega 3 fatty acids and other nutrients that the "standard' formula doesnt have. Having said that, this doesnt necessarily mean it is better for the baby, a lot of mums on here have said that S26-Gold made their babies constipated whereas the regular S26 did not. I did not really find that to be a problem, and you might have to try a couple of formulas (over a month or two period) to find one that suits the bubs if Mamia Gold or any other formula you try does not seem to suit them.
Good luck with it, I have another tin of S26 Gold to go, and then my DD is off formula and onto cows milk............WOOHOOOOO, I never have to buy formula ever again!!!!!! (sorry, its very exciting grin )
His Royal Highness, Prince William