Touch screens are great in point of sale. They are not only faster to use then conventual screens it also is more natural. Rather than look at the screen, then look for the appropriate button on the keyboard, all you do is touch the screen to work it. However, there are some points; I recommend you watch if you are planning to buy a touchscreen in a retail environment.
Check that it is solidly built. Shops are not the most computer friendly environment for a screen to work. It is going to have to take knocks. I had a client where a staff member without thinking rammed into a brand new monitor a mobile, killing both and in the process creating an occupational and health problem. Count on your monitor, being hit, having coffee spills, etc.
What is nice is a stand that can go up and down. What is also better if it can be adjusted right and left so the screen can be adjusted to a perfect position. Make sure that the stand is solid too.
As with all computer gear, check the documentation, few of us can handle Chinese English (Chinglish). If the instructions are terrible and not helpful, you can have continuous problems which may include starting it to work. Since invariably, we lose the instruction notes, check the documentation online. Common problems I have found is difficulty in finding how to access functions like turning off the volume, brightness and resolution of the monitor mainly because monitor manufacturers tend to double up on the buttons so each button does a few different functions eg the brightness and sound control is the same button, who can guess that?
Try the buttons, some monitors, I have seen the buttons that need a lot of force to work, if you do not know how much to apply you can accidentally break the knobs.
Then check the picture text as well as image. If the colour is too bright or the contrast is not good enough, it can be hard to read the writing on the screen. You do not want your eyes having to strain while reading text on the screen.
Check the also here that the colours do not look washed out, as it looks terrible. Also check the glare. Remember you are going to be working on the screen for long periods of time and you really do not want to have to wear sunglasses to use the screen. Also here check whether the screen has a problem with reflection problem, as you are right close to the screen and it makes it hard to read.
The speakers will be little use to you in point of sale environment. Yes, our software can use it but what tends to happen is your staff gets driven mad by the continuous reminders coming for the screen. So I turn off the volume.
Hope this all helps.