doing a plie with your heals together is "like ballet"!
Hmmmmm. If you want to be toned & "sleek" (as a lot of these sites advertise) then a lot of the so-called "Barre " exercises are actually quite antithetical. Just putting your heels together in a semblance of turn out, and then bending your knees, is not a plié. And if you do a fake plié wrongly, there'll be a tendency to build muscles in ways which are not toning or sleek.
A plié comes from first of all engaging your rotator muscles, which should determine the extent of the turned out angle of the feet, and then thinking of sending the knees sideways, while maintaining a neutral pelvis and a completely upright body position, while not sitting in the knee bend, or allowing the knees to collapse inward.
The amazing Balanchine dancer, Suzanne Farrell says that the plié is the first thing you learn, and the last thing you master.
The gym-based "Barre' exercises encourage sickled feet & turned-in legs, and an anterior pelvic tilt. I should think the reason people don't get injuries is because the exercises don't actually push the body terribly much, which is just as well, really.
If you want "toning" and better posture, Pilates and/or Alexander technique are the thing. "Barre" classes are just aerobics dressed up with "ballerina" glamour. But to the trained eye, they're pretty hideous.