I have 24 with springs and 3 without. The spring units are easiest to mount as they snap into the opening left after removing the halogen unit. The non-spring units need to be screwed into the opening, similar to your existing units. They are also required if you have units mounted with very little room between the mounting surface and an above panel such as a cabinet base. Springs can be removed easily. Units are polarity sensitive and have leads ID (+=white and -= black) as shown in photos. Since halogens don't care about polarity, a meter will be handy.
Steve