Those I have seen are used for video. I suppose they would work for still photos as well. I don’t use one and seldom shoot tethered. I travel with a regular notebook and an external hard drive, as well as some DVD’s. Every night the cards are downloaded and backed up, so I am ready for the next day. At the same time I can convert files from raw and check them if I wish.
When in the field, I just check for open eyes and sometimes zoom in to check focus/shake using the camera’s monitor. To check exposure I look at the histogram.