The vast majority of Indian style fast food outlets source all their key ingredients including premade sauces from a franchise.
It makes sense to bypass the middleman. A great option.
p.s. To find the best local most authentic curries I have often asked the taxi driver who he goes to for food like his mum makes. Other than a journey back home many have useful tips. Just note that for those of us less travelled the styles of cooking vary greatly within India and Asia. You need to talk a little more to find out what style appeals. From Very Hot (chillies or peppers) and meaty vs aromatically spiced vegetarian dishes more akin to a thick soup or porridge.
Butter chicken may be revered more for the fact it contains chicken, than the sauce which is just another mildly spiced sauce, when many local dishes are without meats or use lesser product because of the cost.
Every curry is different, and each of us has different tastes, so the best ever curry is really only subjective and relative to our own life experiences. It might help to know what “ best ever” is being measured against? Eg my mum’s Keens Curry with roast lamb left overs and well cooked white long grain rice with English peas and carrots. Yum!
For the rest of us there is always “The Famous Taj Mahal Indian Restaurant”. Just like “The Best Exotic Marigold Hotel” there is an interesting play with the ambiguity of English words.
I look forward to my next trip to one of our two local IGA’s in search of the now famous ‘best curry ever’. Hope they have some goat too!