I mainly give breastmilk but occasionally use forumla and we use Aldi. It’s fine. We use kendamil ready made bottles occasionally too. He has no issues switching . Apparently all formula brands have almost exactly the same ingredients , it’s just different packaging!
The government is currently pushing for supermarkets to put all formula together and emphasise that they are all exactly the same in nutritional value for your baby to try and combat parents being duped into paying a higher price for the exact same product. From what others have said there can be a slight variation in the flavour so baby might have a preference for one but overall they all meet the same strict nutritional and safety standards. On transitioning, I've never done it as I've always ebf until 6 months then added follow on milk here and there but I've been told that it takes about two weeks for baby to adjust to a different formula so not to be deterred immediately
I bought one with the intention to swap as it is essentially the same ingredients but half the price! I mixed a scoop in a few bottles to try and transition and my LO had the worst runny poos ever so I went back to aptamil. It might be that I should’ve persevered and he probably would’ve adjusted but I decided not to mess him about and just bite the bullet of the higher price 🤦🏼♀️