A HELOC has a replenishing feature, similar to a credit card. When the borrower pays down the principal, they can re-borrow up to the amount of the line. Plus, you only pay interest on the amount advanced. On a HEL, the full amount is advanced the day the loan is originated, the borrower can’t re-borrow as they pay down the loan, and interest is charged on the full amount of the loan.
The replenishing feature makes the HELOC much more flexible than a HEL. However, as you stated, the HELOC might carry a slightly higher rate. Plus, a HELOC requires a higher level of discipline from the borrower because the required payments won’t amortize or pay off the line as quickly as a HEL.