It works. Lovely white results. Although crowns, veneers or any non natural items in your mouth will not whiten, so careful of mismatched teeth. Have zoom done before any dental work so the colour can be matched to the whitened teeth.
Sensitivity - It hurts a bit. The pulp(which discolours with age) is also whitened. The sensitivity feels a bit like electric shocks in the teeth. Try nurofen or relief gel, even toothpaste for sensitive teeth to relieve it but calms down in a couple of days. Cant eat any highly coloured foods for 48 hours after until tubules(microscopic holes in the teeth which lead to the nerve) close up again after bleaching otherwise you will stain the teeth.
Top up in 6 months with syringe of 22% bleach about £22 to put in your trays for 20 mins a day until the colour comes up again. Zoom should only be done in a dental surgery because the soft tissue must be properly protected as the bleach can burn, blistering your mouth.
Careful of cowboys. Cost £400 with trays
Nice results finish by buying yourself a fabulous lipstick to frame that bright positive confident smile. Your best weapon is a killer smile!