I've been in the electronic business for a long time. I used to buy Sam's Photofact for my needs which intailed having to go to the store and paying about $20 for a package of 3 different units so I was forced to buy more than I needed just to get one.
Owner manual is just at your keyboard and the information is almost instantansouly and the cost is very reasonable. Easy to print out if needed or simply read off of the screen. The larger the screen the better for obvious reasons.