I'm not sure what you do or don't know so forgive me if you're already aware of any of this (and I could be wrong). Madras Curry Powder, particularly Rajah brand in the UK, is often a single ingredient in a BIR Chef's personalized 'Mixed Curry Powder' or 'Mix Powder' along with 4 or 5 or even up to 6 or 7 other spice powders. There is a whole section of the forum devoted to the subject. Chef Syed's recently published powder is the first one (as far as we know) to present a dry roasted powder recently and from memory it contains no Madras CP at all. I'm not sure if any use Rajah CP straight out of the bag. I guess some chefs / cooks may do but it isn't commonly discussed here as normal practice.
As far as I'm aware, using Madras Curry Powder does not necessarily make a Madras Curry (or at least not a BIR Madras), although you'd think it should. A Madras can be the name of a dish. eg Chicken Madras, or it can refer to a particular target Chilli heat level for any dish. It is all very confusing and there are no rules.
As for Madras Curry Powder, Rajah is not readily available to me as I'm outside the UK. I use Clive Of India Authentic Curry Powder as a family favorite (not labelled as Madras) but lately I've also been using Mother's Recipe Madras Curry Powder (in a green can) which I find very nice. Another popular green can is The Original Ship Madras Curry Powder. You can also find recipes online to make your own Madras CP including a copy of the "one in the green can". When I researched this I found about 5 or 6 different brands sold in green cans.
Anyway, good luck and simply cook and enjoy whatever it is that you like.