How deep you can get still depends on the person. Using it over time is supposed to train the mind to achieve these states easier. You are right that you still need to keep your concentration. Its very easy to just let go and let the mind wander. All in all, if your (sp?) serious about meditation I don't think its a substitute for the old fashioned way. I use it to get myself relaxed before meditation. If you have the expendable income it might be worth looking into. If not, I wouldn't make it a priority purchase.

There are some articles at the link you might be interested in reading.

http://mindplacesupport.com/Reference.htm

Rich