I see the American reviewers are much more positive about the mat than the British. But I agree with you Americans on this point.
I have used it naked (otherwise I can't feel the spikes) and up to an hour at a time, though I began gradually.
At first it feels extremely painful. though I suspect this appplies only to us unhealthy people who are already suffering from this and that and have intense need of stimulation of the various points. (My 12-year old granddaughter when trying out a Shakti cushion claimed she felt no pain when using it while other members of the family - adults - felt it to be extremely uncomfortable.) However after about ten minutes, generally, the pain subsides and one can hardly feel it. In my case, however, when using the mat on the buttocks, firstly, it was more painful than usual, and secondly, the pain at first did not subside, though it does now slightly, though only after a long time.
When exposing only the back area to the mat, after about ten minutes I generally feel a wonderful, extremely comfortable inner heat spread throughout the area, similar to leaning on a hot water bottle, but as stated a deep inner warmth. The feeling is almost orgasmic - it feels like the exposed cells are feeling ecstatic, and extremely satisfied. This is a wonderful feeling - in fact I'm becoming addicted to use of this mat!
I suffer from MS and several other auto-immune diseases. I had had most of my left buttock numb for several years. After about three applications of the mat on my back (not buttocks) suddenly my left buttock felt normal. This was fantastic. Also when being scanned with something called Meta therapy (a treatment used in Russia and other East European countries for about 20 years in their hospitals - something I get done regularly in Denmark where I live - but not administered by doctors!), it could be seen that my heart and circulation were extremely improved, apparently functioning perfectly. The therapist found it amazing and told me to use the mat twice a day from then on. However, I don't generally do that.I use it when I can, and when I feel like it. But the improvement that occurred did so after only a handful of "treatments".
Sometimes I feel extremely relaxed after using the mat, though I don't always notice this effect.
I'm not saying this mat is a miracle worker, but it definitely has an extremely beneficial effect, and I feel that users should try it out on various parts of the body. I feel that the more health problems one has, the greater will be the benefit. But even if you do not suffer from severe health problems, use of the mat will surely have an immense preventive effect.
I recommend it highly. Who knows what its use could lead to in the way of dramatic health improvement?