The description sounds like they're talking about dragging the mouse over screen images, but your reference to "the fiddly scanning" suggests something more like scanning off of paper(?).

Assuming you mean scanning from books or prints:

There are a number of scanners apparently similar to what you've described, and they're apparently handy for some fairly specific kinds of of material. The most frequently claimed use is for books that you can't lay flat on a real flatbed scanner (or can't take home to do it right, as for reference books at the library). This sort of assumes that you're carrying a laptop or smaller semi-computer.

Some of the "passover" scanners include memory so that you can take just the scanner with you, and download the scans "back at home." With those, of course, you can't look at what you got until you hook up to a computer (or in some cases to a printer). These range from the size of a "pencil" to "bars" that will cover up to an 8+ inch wide sweep.

Most of these have the general difficulty that variations in the speed at which you move the scanner can warp the image, and with the smaller ones it may be difficult to maintain straight line scans or even "smooth arc" motions. The "modern" versions incorporate some ability to "correct" for some irregularities in motion during the scan strokes, and many include "stitching programs" to put the bits together prettty much authomatically; but from what I've heard (without direct experience) it still takes some "operator learning" to be able to use them really effectively. The "correcting and assembling" programs of course go on your computer.

Reports are that scanners in this general category can do a "good enough" job on text, if you're just taking notes for your great novel (probably just what you need), or keeping receipts for the IRS (maybe?) but if you're doing other than Facebook posts with images I'd be inclined to use a "real scanner" (or maybe even a phonecam).

You'll want to look very carefully at the specifications, ignore the "user ratings" mostly, and download and read the operator manual before spending many bucks for any devices like the one described (but of course you'd do that anyway). If the thing is "really cheap" of course hands-on is the best way to know how badly you got conned.

Some of us here are old enough to remember when we'd never heard of "LG," but they've established enough of a reputation to be fairly well recognized now, and probably will be around longer than the warranty you'd get on any of their stuff. I haven't seen a lot of comment on their "user support" but they've had web sources for enough information to check most of their stuff out - at least as well as for anyone else's.

John