One of the biggest benefits to receiving payments via echeck is that you have no fear of half a year later being hit by a credit card chargeback, since the payment was funded directly from their checking account.
One thing I would recommend though is when you contact the buyer to let them know that you will ship after the echeck clears, advise them that if the bank account that funds their PayPal account has a debit card associated with it, that they can use that card on PayPal as if it was a credit card, and payments would be instant. Effectively the same funding source, but no echeck delay.