'handy gadget' is correct and usable in written English.
You can use it to refer to any small, useful tool or device. For example, "This new handy gadget makes it easy to clean up quickly around the house."
The cyclist's handy gadget – make flitting between meetings disaster-free with this lightweight multitool for frequent cyclers.
It would be a handy gadget for the recipes Jonathan Swift included in his notorious essay, "A Modest Proposal".
Nick had packed a portable satellite terminal to ensure we could connect from anywhere – a handy gadget, especially when the New York Times is paying for it.
From a graduate incubator space at his alma mater he has developed a wall-mounted storage unit called the Geco Hub and the Nimble, a handy gadget for opening packaging and cutting sticky tape.
A tranquil cylinder of "delightfully resonant metal, it could be opened in an instant, requiring only the application of a handy gadget freely dispensed by every grocer... Now we are given instead, a top beeling with an ungly, shmoo-shaped "tab," which after fiercely resisting the tugging, bleeding fingers of the thirsty man, threatens his lips with a dangerous & hideous hole.
This handy gadget monitors your dog's health and makes suggestions for ideal activity levels based on size, age and breed.
(Travel routers are handy gadgets if you're only carrying a smartphone and tablet, neither of which have proper Ethernet ports).
These handy gadgets, used to sweep crumbs off the table, come in more permutations than you can ever imagine, including one that is described as "aircraft grade" and another that can be monogrammed.
These handy gadgets are used to pick up the frequency of a bat's echolocation signals and so identify its species; some can be used for digital recording too.
By 2003, however, all these handy gadgets might be obsolete.
USB card readers are handy, handy gadgets.
