I don't know anything about Zoom so I can't comment on that, but I do have a set of bleaching trays and have had them for about 10 years. I used them, originally, over the course of two weeks, until I got the desired results. Some solutions are made for overnight use - you just sleep with your trays in. I didn't want to sleep with anything in my mouth so I was fine to use them a few hours in the evening for that initial couple weeks.
Every few years, I purchase a new bleaching solution kit from my dentist and do a touch-up. My beverage choices stain my teeth over time. I've used the kind that your previous post suggested and I've used the professional Crest brand (whichever my dentist is suggesting at the time; Your previous post in the dental field may have a better opinion of what a better bleaching kit may be.) It may take me a few days to achieve the desired result. The last time I purchased the touch up kit, it cost about $25.00. One of my friends, with the counsel of her dentist, whitened her teeth that had been discolored by taking tetracycline at a young age. She used the bleaching tray method for the process and was pleased with the results.
I like doing it this way, personally, because you can control the desired results and it looks clean and natural. Probably my biggest fear of whitening my teeth was that I never wanted my teeth to end up looking like Chiclets (gum). Too white of teeth just doesn't look real.
Hopefully others may be able to give you more guidance on the "Zoom" method.
Good luck whatever you choose!