Elo accounts for a lot of the touchscreen technology that's been out there. It was / is used on a lot of OEM monitors.
If you don't get drivers with your purchase, make sure you get enough information to download some before making the purchase. Do ALL of your research ahead of time.
Old TS's are mostly serial, but you'll need specific drivers to use them. You can't roll your own easily.
Resistive touchscreens are a double layer overlay, so they inherently aren't as sharp as the capacitive style which is usually an evaporated coating on a glass plate.
Resistive touchscreens are durable, but can be damaged more easily. They all should be cleaned carefully and as often as required.
Resistive touchscreens can be used with a pointer or gloved hand, while capacitive need flesh.
Most are just ordinary VGA with a separate connection for the TS stuff.
DB-9 cables are DB-9 cables. Just make sure that the unit has the power cable / adapter if one is required. Newer ones will use USB, but if you are looking for cheap / old, then it will most likely be serial. Some are powered by the PS/2 port through a splitter, so you might want to make sure that all of these things are discovered and included before purchasing.
RandyT