I replaced the battery in a 15" mid 2010 macBook Pro, which was very easy. I also replaced the battery in a 13" MacBook Pro which was not easy for an old timer but made easy by iFixit's repair manual.
I bought both batteries from Apple but it turns out they sent me the wrong one for the 13" which I then found at iFixit. It was the right part and it was cheaper! The iFixit ProTech tool kit is worth the cost. And iFixit follows up to make sure the customer is satisfied. Very satisfied. 10 out of 10!!
I would say that for older people, the iFixit repair guides are very easy to follow and you always know where your package is in the delivery chain. My unequivocal recommendation!