First time was insane, it has definitely whitened my teeth over the 7 days I've been using this due to me always smoking and drinking. No sensitivity so that'd a plus. NOT THAT MESSY, ive read its messy but it was just easily rinsed in the sink. Customer service was great, I actually put the wrong address (my fault) and they sent another one no cost to my correct address, that right there is why im even taking my time to write a review most companies don't care these days, overall I love it and will definitely use it for life.