Tremco is easier to install, but I don't like that a key is left in the ignition that could be taken. The Able 2 Ignition override does require a button to be pushed before removing key. The brake pedal will disengage override rendering the vehicle simply parked in the event someone tried to drive it. If the key is inserted and turned to the "run" position, the car will drive normally when the brake pedal is pushed.
Very easy to install and will work for almost any vehicle with some thinking. Are manufactured to work with specific emergency vehicles but I have used them on others. Good people, great support, and reasonably priced.
I've got one of these on my Explorer. Didn't need all 4 relays, but it's what was available when I purchased and the price difference was small. Requires a button push, then take the key out. Vehicle dies if anyone pushes the brake pedal to shift into gear.