Electric brake draw backs. Most need electric to release. Meaning if you loose current while in motion? The brake will come on very hard. Seen electric brakes on MPE Yales & Hysters actually throw the operator off the truck while in rabbit speed. When hitting a bump because of a bad battery coupler. Also yes some trucks have release bolts & tow switches. Hysters & Yales have a brake jump out plug on walkies & 3 wheel trucks & Stand up end controlled trucks. Some have juper plugs available to buy. All need at least 12v to release brakes. If batteries go dead in a unit like a walkie on a delivery truck? Jumping the plug will not work. So the driver needs to carry a 12v jumper pack. With a mech. brake you could move the truck. With electric brake. Without power the truck has to be picked up. Hyster & Yale are still having a lot of issues with electric brakes burning up. Electric brakes are easy to service. But I think the mechanical brake is still better operating. They are gaining on it though. On the new 3 wheel AC trucks. They are using a electric brakes for parking & Mechanical wet brakes for service brakes. Also on all trucks 3 wheel and new IC trucks with wet brakes they are using hydraulic tractor oil in master cyls. Seen techs already making mistakes putting in dot3 or 5. Which causes leaks internally in drive units. Due to brake fluid not being compatible with gear oil in drive units. Electric brakes are on or off. Restraint can be adjusted on some. But the old enemy is still there HEAT! Take your pick here? ETS.
Randal you are quite right about smoothness of operation, but those out there in the market currently that I have driven are not the best....but we are making steps in the right direction.
Electro-mechnical (Hydraulic) systems can be designed to allow the brake to be 'pumped off' using the steering system in a manual mode for pressure, which means that even with a dead battery the machine can be moved.
The smootheness of operation could be designed into the operation if driven by consumer demand.
The one disadvantage of an electric braking system is moving the machine without a battery, even this obsticle can be overcome such as in the Raymond Order Pickers there are two bolts mounted beside the drive unit to release the brakes with. The Crown Order Picker has a DRIVE/TOW toggle switch which is great if there is power left in the battery but falls short of the mark in the case of battery failure or absense.
You've said electromagnetic, but the most common I think would be electromechanical for these models.....?
From a maintenance/cost point of view the mechanical brake wins.
But in terms of function and benefits the electromechanical or electromagnetic they would come top.
Any electrically controlled system can be made to do what the controller wants it to do and this makes it flexible, where as a manually controlled system relies on an input from an external force. Features of such systems are holding a machine on a ramp without operator input, preventing rollback on a ramp by locking the brakes and allowing power to be applied before releasing the brakes, applying the brake when machine is switched off or left unattended.
I am not a particular fan of electromagnetic brakes because of how harsh they can be in applying and releasing.