An e-check is well a check you could easily prevent the buyer from ever gaining access to the funds in a number of ways, including but not limited to placing a stop payment on the check before it processes on your account, later claiming you did not authorize the transaction, withdrawing cash from your account prior to the transaction posting to your bank account. Additionally if you were engaging in something like check kiting then your bank may display a higher available balance then you really have and the bank will ultimately not pay the check.
Above all of this, there is no guarantee that the OP can legally write checks off of the account he is sending funds from and as a result anyone selling bitcoin from him would be receiving stolen funds (which would not only be reversed from your bank account but could also start a criminal investigation against you).
tl;dr - don't deal with the OP
edit: contrary to popular belief, there is no such thing as a check "clearing" the banking system. Banks will sometimes delay the availability of funds to your account for a certain amount of time that it will likely take for them to receive notification of any reversal, however a reversal can be done long after these holds have expired
