Well here the math I do to see the economy side of using ADA liquid ferts comparing to other brand liquid ferts commonly available here in Malaysia.

Ferropol 250 ml = RM 29.70 (East Aqua after 10% discount)
Dosing suggested : 5ml/20 liter (weekly)

Hagen Plant Gro Iron Enriched 250 ml = RM13.00 (88Marine, etc)
Dosing suggested : 5ml/35 liter provide 0.3 mg/l iron (weekly)

ADA Brighty Step 2 250 ml = RM 56.20 (some give 5% discount)
Dosing suggested : 1ml/20 liter (suggested 3 times a week)

Each liquid ferts rich with iron and potassium.

Although Ferropol and Hagen suggested the dosing for weekly, they also suggested to increase the dosing in order to maintain enough trace (iron 0.2-0.5 mg/l) based on plants requirements.

So let assume that we dose trace elements 3 times a week (EI) for our heavily planted tank. Also lets assume the tank is 100 liter tank with hight light, heavily planted, CO2 enriched.

Ferropol = 25ml X 3 = 75ml, Cost 75/250 X RM29.70 = RM8.91 per week
Hagen = 15ml X 3 = 45ml, Cost 45/250 X RM13.00 = RM2.34 per week
ADA = 5ml X 3 = 15ml, Cost 15/250 X RM56.20 = RM3.37 per week

You may dose a bit less Ferropol or Hagen since the dosing is for weekly, but the economy side of it still show minor differences in a long run.

So make your own conclusion.

I hope my calculation is correct. Correct me if I am wrong. And I am not promoting anything here, just to show the fact. Just my 2 cents.

Thanks