I love these outfits, especially the colours of #2. This exercise answers the how to wear a fair isle sweater question and retain your signature, polished style, which you have done to great effect.
Whether you should get a fair isle sweater is harder to answer, because it is a question of "When would you wear this?" and is this a look that you would like to add to give you some more casual options. I think a lighter gauge sweater would look more refined and so you may find those even easier to style that these two oversized sweaters.
Often when I am looking at something that is outside my normal style I think of how it makes me feel and if I ran into an old friend would I be happy if they saw me wearing this. Embracing a new trend is fun, so there is definitely no harm in giving them a try or even borrowing these two beauties!