The amount of people who still sext with Snapchat are probably equivalent to the amount of people who still play Words With Friends. In other words, not most people. Using Snapchat lusty horny swingers parties sext is ancient history because of ( as you probably already know ) screenshotting - even if the shot only lasts two seconds.
The only snag with the free sites is this. There can be a lot of losers on there, people who only use them because they are free and cannot afford to pay to use the others. No good if you are well heeled and afluent and not wanting to meet someone who will sponge off of you.