I picked these up in Boots for around €18 which was on offer. You get a one-week supply which is 14 sachets containing two strips each and the accelerator pen. They recommend using these twice a day for a full week but, I just use them about once a week so I get better value from the box (I've even tried using only one strip and saving the other but, the strip doesn't last out of the sachet!).
The accelerator pen is a new one on me. You wipe your teeth dry, dab the pen onto each tooth you want whitened and then apply the strip. I presume it is supposed to activate the strip/expedite the whitening process but, who knows!
The strips do work. It's not a bright, white American smile but, it is a subtle "Oh, your teeth look white" type brightening. My issue with these is the taste. They say mint, I say disinfectant . It's absolutely vile and I gagged the first time I applied the strips. However, I have gotten used to it and can stomach 5 minutes of tasting what reminds me of the air in a hospital for a nice, relatively cheap, white smile!