Squirrel won't negatively impact your credit score. For people who we help budget and repay debt we actually see the reverse, where your credit score can improve. Likewise if you need evidence of income for a mortgage we can issue a statement of your account you can use.
Squirrel shouldn't impact your free banking, as all your money still goes into your bank account, it is just spread across the month. This only won't be true if you save so much that you dip below the amount required for a free account. This rarely happens to our customers.