The reviews are all over...Unfortunately, people's grout lines are discolored permanently mainly because of products (vinegar & Clorox) they've been using in the past...
If you're looking to making money in color sealing, this isn't the product you should use I'd recommend
www.thisoldgrout.com or
www.colorclad.com better products.
Prepare your grout lines properly before any color sealer gets applied with alkaline than acid wash...Color sealer is not a product to stick to un-sanded grout...Sanded only!
I never liked color sealer, as you might read from my past, however, it's about making the money, and making someone's life miserable in the future (homeowner or service)
Have you seen Mark Marckonic's New color sealer tool? Looks interesting enough to try...Certain grout joints are better than others for application BTW...
I define color sealer as a temporary solution to a permanent problem, eventually...
The best case scenario for color sealer is for someone who has discolored grout lines prior to selling there home and color sealer is the cure-all...New homeowner is unaware of color sealing. and now has peeling and uplifting and now what? A problem for someone to ponder...
Best of luck!