I have also only used the regular step as well but after researching about the Easy Tone I would be interested in that as well. Like Christine mentioned, it may depend on your experience with using steps and doing step workouts.
There are certainly advantages of both; the regular step is pretty much bomb proof, especially in a home setting and there wouldn’t really be any durability issues. It also has an adjustable height to increase or decrease the difficulty of various exercises. The advantage of the Easy Tone step is in it’s versatility including more exercise variations and core involvement. Since I haven’t used it myself I am unsure of potential puncture issues, but I have used products made with similar materials (such as BOSU) and haven’t had any problems.
If I was choosing for myself I’d likely go with the regular step; mainly because I have plenty of other fitness tools and accessories to use for instability exercises; but for an all-in-one (assuming no durability issues) the Easy Tone might be a worthy piece of equipment.
Both are often available through Perform Better here: http://www.performbetter.com/?kbid=4524&img=pb_banner_300x250_9-28-2010…. – if you do a search for the Easy Tone Step there is an available video showing what else you can do besides the traditional step exercises, if that helps with your decision.