Yes, check out that link I posted. There is a penalty for selling in the first five years - - it is more significant if you sell in the first year, if you sell in years 2-4 it is pretty minor. For this reason, we are gradually shifting our "extra padding" emergency money to i-bonds rather than making it the core of our emergency fund. I would aim to shift in small yearly increments or every other year to lessen the liquidity concerns. Once you are outside of the five year holding period there is no penalty.
ds 2007
dd 2010
baby dd 2014