I use them for my type 2 decks. For newer cards they fit better into the newer sleeves than old ones as the inner perfect fit sleeves are supposed to be a tight fit and not wiggle like they do older cards. The scrunching that can occur is partly just due to the material for the inner sleeves but the newer cards haven't given me an issue there. The older cards however are a pain to get to properly stay in an inner sleeve when trying to put them in the normal sleeves. I've found I basically have to hold the inner sleeve with my finger to the card it self while inserting it into the sleeves so that it doesn't move. I have small fingers though so I can do this. I can be a difficult process and the worthwhile nature of it is debatable. Yes it will protect your cards more from things but the time money and effort required will not likely be worth it for most. Honestly I do it because I think doublesleeved cards have a cleaner shuffle, it protects corners more since the outer sleeve corners have the potential to split (I split a dragonshield at Nats in fact), and because it's a bit of a habit from another TCG in a format that had 100 card decks.
As for tips for the process itself. Take your time, make sure the inner sleeve is flush to the top when putting it in the outer sleeve, try to hold the inner sleeve to the card itself, and you may have to open the outer sleeve with your finger or something like that just so the corners/edges of the inner and outer sleeves don't hinder the process as much.
