I haven't done the whitening pen, but I did do the regular BriteSmile (costs around $500). I believe the pen would be the equivalent to the other products on the market, just depends on the cost.
When I started wanting my teeth whitened, my dentist told me to try Crest White Strips (premium). He said that he'd much rather me spend $30 than $600. If the strips work, then the dentist can improve upon that up to three shades. I did the strips and was amazed! I then wanted more! I chose BriteSmile because it is done in one trip and you don't have to use bleach trays every day.
I also tried other "paint on" whitening products. I thought they were nasty and made me gag. Like having mucus in your mouth (sorry).
I would compare costs. Pen vs. other products on the market. There's even an article in Consumer Reports which rates the products!