Paypal eCheck are basically just funds transfer from the paypal bank account to pay you instead of using their credit cards or their paypal balance. It should be as safe as any means of payments through Paypal. It is best to wait till the eCheck is cleared before you deliver.
One of my hosting clients paid me yearly hosting with an e check. paypal told me that the echeck has been recieved and its not cleared yet and will take a week to get cleared.So i shouldn't give him any service unless the check passes. but i thought that i should give him the account just as goodwill and trust, so i provided him an account an everything and after a week he just cancelled the payment. Only because he found some free web host. Though the echeck cancelled , i gave him a day to backup the data. Echecks really scare me after that.
It is just like any other check your business receives, you need to make sure it clears first and then do the service. I know many people getting scammed by this especially on Ebay by people sending e-checks and people sending out the product and once product is received then the e-check is canceled. Paypal has taken steps to prevent this with making it harder to cancel the check such as having to fax them a ID of the account owner and some other security measures.
I think the checks are a little better because they take less fees out of them. The checks are safe, just don't give the product until the check clears. Another option is Escrow.com.