Depends on what you mean by "work."
If by "work" you mean, do you lose weight doing them, then answer (for me!) is YES. I lose weight as well or better with Leslie than I do with Cathe (although I like mixing them up.,)
If by "work" you mean, do you feel good doing them, then the answer (for me!) is YES. One of the main reasons I work out is stress relief, and Leslie works very well for that because her chit-chat is always positive, and longer, steady, lower intensity cardio really is a great mood booster for me (although more choreography also reduces stress for me, in a different way, by keeping my mind FULLY OCCUPIED for awhile.)
If by "work" do you mean, improve your cardiovascular capacity, probably not, if you are used to doing more strenuous workouts. However, you might be surprised how
little of that cardiovascular capacity you actually lose when you take it down a notch in intensity.
I'll be interested in hearing your report after a month of Leslie and Ellen!! I bet you are going to feel great.
And I bet you'll find that the fitness world doesn't fall apart when you lower the intensity for awhile.