Here's more info on Arbutin:
While some promoters hail arbutin as a completely novel skin-lightening agent, it is actually hydroquinone in disguise. Arbutin is glycosylated hydroquinone (b-D-glucopyranoside derivative of hydroquinone to be exact), i.e. its molecule consists of hydroquinone connected to glucose. It is believed to work by slowly releasing hydroquinone through hydrolysis, which, in turn, suppresses melanin synthesis by inhibiting the enzyme tyrosinase. Arbutin appears to have fewer side effects than hydroquinone at similar concentrations - presumably due to the more gradual release. The range of arbutin concentrations reported in the literature is 3-7%.
Arbutin clearly has some pigmentation reducing effect. Yet, it remains unclear how well it stacks up against hydroquinone and what the equivalent concentrations (in terms of effectiveness) of these two agents might be. Arbutin appears to be gentler than hydroquinone as far as typical side effects like skin irritation are concerned. However, it is unclear whether the concerns recently raised regarding hydroquinone (risk of ochronosis and possible cancer risk) may apply to arbutin as well.
Finally, due to patenting issues, many skin care companies use arbutin-containing plant extracts (such as bearberry, blueberry, cranberry and other extract) instead of pure arbutin. Whether such products contain sufficient amount of arbutin is unclear. Even if they do, it is unclear whether arbutin in plant extract is equipotent to standard arbitin. (For example, plant extracts may contain other substances interfering with absorption or activity of arbutin).
All in all, arbutin appears to be a promising hydroquinone alternative, but many uncertainties remain.
Source: Smart Skin Care: Treatment of hyperpigmentation problems / skin lightening