These options are just as simple as they sound. Do you want to manually lift the heat platen every time the timer goes off or do you want the unit to release automatically? With that said, there are factors to consider.
The manual release presses are typically less expensive than the auto-release counter parts. The auto release feature is only available on clam shell style presses. Therefore, if you want a swing-away style press, you will need to go the manual route. With a manual press, it is not difficult to release the heat platen at the timer or any time before. If you want to stop an auto-release press mid-cycle, you have to release it another way outside of the handle. This can be difficult or dangerous.
The auto-release feature is a great option to have if you have a good deal of production, as it improves efficiency. This feature is great for smaller shops where the owner or employees wear many hats and can sometimes be pulled away from their heat press duties unexpectedly. When the timer goes off, the press releases and opens on its own so you can walk away and not worry about scorching the garment or item you are pressing. One major drawback to the auto-release is that the pressure of the top releasing can be a little more aggressive and abrupt compared to opening the press manually. This can cause the item you are pressing or the transfer to shift, a common issue called ghosting, especially with sublimation transfers.
—2 Regular Guys, MontCo Consulting