Endless Slideshow Screensaver offers 30 transition effects in the free version and more than 240 in the Pro version. You can preview and select which transition effects to use during the slideshow in the screensaver settings, [ Slideshow ] tab, [ Transitions ] section.
If you want to see a preview of any transition effect - simply select it in the transitions list, like this:
If you want to use a certain transition in the slideshow then check the box near the transition name. If you don't want to see a transition - clear the box near the transition name:
You can use the [ Select all ] button to check all transition boxes with one click and the [ Clear all ] button to clear all transition boxes. If you clear the [ Enable transitions ] box, then one slide will be replaced with the other without any transition effects.