CTC's chambers are the best I've ever used. I've used all of them, and these have a better seal, are more comfortable, are lighter but still strong, and just produce better stretch and pump regardless of electric or manual. I didn't expect there to be a difference but there is. More thoughtful engineering is demonstrated with these, and the slight slope to the insertion end may be the slightest detail that makes all the difference. The comfort gasket is excellent, too. You'd think others would have this, but alas...not the case. Get several sizes, because you will grow fast and can save money. My favorite chambers above thick wall or elliptical. If CTC ever makes an elliptical...get it, too. Very impressed. Pleasureful and very functional...