I work at one in SA currently, while I am studying. I'm just a...

I work at one in SA currently, while I am studying. I'm just a part-time worker so I don't see anything behind the scenes so take what you will from this.
I 100% agree with you that the marketing team and real estate or whoever finds the locations do a fantastic job.
In SA, compared to other states like Queensland, we have only had a few stores and in the past few years and not that much brand awereness. From my experience, Zambreros is more popular here. However, recently, GYG has been aggressively opening new stores in high traffic locations and been heavily pushing different promotions. E.g. For each new store, they'll do a free burrito day or 5 dollar burrito.

In terms of reviews, i personally find you only review if you have an amazing or terrible experience, so it can be quite misleading. In terms of value for food, $3 tacos and coffees are great as well as the mini-meals. If you don't think the food is quality based off of some reviews, maybe go and try it and see how it goes (My personal fav is nacho fries, chicken with chipotle mayo).
I think I remember seeing or hearing (I think possibly when equity mates interviewed the CEO steven marks on their podcast) somewhere the goal is to get 500 stores in Australia and only have 135 current stores. With the GYG still growing within Australia and already doing 1 bill in sales, I think this could be a fantastic investment for Magellan.