Screen size. It might be tempting to save money by choosing a DVD system with a small screen. We caution against buying a player with a screen smaller than 7 inches. You won’t save that much money and viewing images can be difficult or uncomfortable, particularly if two people will be watching.

Display quality. Compare the picture quality of different products before buying. On portable DVD players, screens that can be tilted or swiveled can help you find the best viewing angle, particularly in brightly lighted environments. Most models now have wide-screen displays that mirror the 16:9 format of movies.

Sound quality. If possible, listen to the system through headphones. For improved sound, consider purchasing better-quality headphones separately. If you won’t be able to test the model before buying, strongly consider a retailer with a no-questions-asked, 30-day return/exchange policy for portable units.

Monitor location. Many systems have a monitor that folds down from the headliner and is located between the two front seats. Unfortunately, this can block the driver’s view out the back through the rearview mirror. A better monitor location, from the driver’s point of view, is in the front seat head restraints or near the center console, but this could require a custom installation.

Mounting system. If you plan to use a portable DVD player in a car, be sure you have a mount that will keep components from flying free if you brake hard or are involved in an accident. If the unit doesn’t come with an adequate system, you can buy a mount for $20 to $40.