Spot on!
When I work with a beginning player, I'll teach them the pendulum swing. It is a far easier stroke to learn and I do believe that it can be a superior stroke to a pendulum in terms of accuracy. Try this experiment if you do use a piston stroke. Shoot the famous up and down drill with the cue ball. Place the cue ball on the spot and shoot it straight down to the end rail on the vertical axis. Use your normal stroke (if you have elbow collapse), a few tries and then try it using a perfect pendulum swing. In my own experience, I seem to be more accurate using a pendulum swing.
For the few arguments about not being able to generate power using a pendulum swing here is a video from everyone's favorite instructor the Oyster:
https://www.youtube.com/watch?v=3GsRIPSTWfo
Now with all of that said, I've decided against making the change to my own game for a couple of reasons. I've developed a fairly repeatable stroke over my 30+ years of playing (Hamb Method). It is a piston style stroke that was developed naturally by trying to keep the cue level on the follow through.
There are two reasons for my decision not to make the change. First, changing your stroke will take a lot of practice and time to be able to perform without thinking. How much time? One top instructor guesstimated a week. Scott Lee in an earlier post on this thread estimated one to two months. A top regional player that also is an instructor has been working on this change to his own game for four years and still struggles with it (in his words). Personally, I worked on it for a week and I know it would take me much longer to be able to do it without thinking about my stroke.
The other and more important reason to my decision not to make the switch is that it does change how the cue ball reacts. I'm not sure why, but If I want the cue ball to go to a certain spot using a pendulum swing it doesn't quite go where I think it should but using my old method it would if that makes any sense. I would have to learn two new skills, the stroke and cue ball control.
The tip will tell you what you are doing on the swing. Pendulum it will end up in the cloth. Piston it will stay at level of where you are striking the cue ball. The tip should be at level or lower. If the tip is higher than where you initially struck the cue ball then the shoulder is involved which is almost always a no no. There is one top player that uses his shoulder in his stroke, Mike Davis, but of course he has grooved this stroke with the Hamb method.
The one change that I have made to my stroke is to make sure the tip is a level or lower. On certain shots, such as hitting the cue ball with high karate (extreme high where the bottom of the tip strikes the cue ball with speed) I have a tendency to let the tip go high after contact. I've been working on limiting my elbow collapse with some success.