If you've ever seen a presentation where the slide changes are punctuated with the speaker saying "Next Slide" "No, go back." "Wait, two slides forward." Then you know how nice it can be for the speaker to have their own buttons to push. Just be careful to rehearse with the button pushing so that it is natural and smooth, not distracting or obvious. It should look like the slides appear at your words, not at you fumbling to find the right button.
As far as what you should get - I have a few thoughts that I hope will help you decide.
- Make sure that you need the features on the presenter. I've seen some that have so many buttons and options that it becomes difficult to navigate during a sermon. This one is especially confusing because it has a mouse built in - if you click the right mouse button then it will stop your presentation, but below that are the forward and back ward buttons where you need to click the right button to advance the presentation.
- I never use a timer or a laser pointer in a sermon, but they are built in on a lot of presenters. Don't waste your money on these options.
- Make sure it is a radio frequency (RF) device so you don't have to be pointing at the receiver in order to advance your slides.
- Get a 'black screen' button - it's very nice to be able to turn off the presentation for a bit so you can make your point without distraction (if you can't get this then just insert black slides in your deck).
- Make sure you have the range you need - most are 50 feet, but if you have a larger space you might need more range (it'll cost you).