First, the cost is not close to the same.
Meth kit ~ $800
ATP turbos ~ $2400
EPP upgrade turbos ~$1600
So, the parts themselves are not close in cost and then you have install. After laying under my car for a few hours changing the dowpipes, I have zero interest in changing the rear turbo unless I HAVE to. It would not be a fun job!
Meth installation on the other hand is merely time consuming. You will spend hours running lines, mounting things, etc, but trust me...it's not the same as doing that rear turbo.
Then you have the final product. A meth kit solves problems by giving you a lower intake air temp and cleaning the intake manifold and tops of valves. Provided you are able to dial in the tune, you will have a happier car.
With the upgraded turbos you will have more heat, provided you up the boost, and more serious tuning needed, plus put you closer to maxing your fuel system.
I could be wrong, but it would probably be hard to find someone with upgraded turbos without a meth kit to help with heat and provide additional fueling.
Edited to add...I don't even have a meth kit on my shopping list, but do appreciate the effectiveness. Personally, I'd like to see a front mount intercooler option more than the other two items.