Of course these cost more than $1.78 to make and far more than that to ship; there is no free lunch. The money comes from elsewhere.
It seems to be some sort of loss leader on the AliExpress iPhone app. I do not see these deals on the web site. You have to choose 3-10 of these "special" items and they claim you get free shipping. Where I live I pay 10.5% sales tax, but Aliexpress adds about 18% for the tax. I suspect some of that "tax" amount goes to cover the shipping.
When I bought the meter it was $1.78, but most times the offers are for $1.99, $2.99, or $3.99. If you look at an image from the iPhone app today you can see the meter is $1.99. I bought one of the $1.99 AppleWatch chargers for my wife and it works great.
The meter I bought was defective, it shows a low battery all the time. But you may get lucky and get a good one. I have made for of these orders and "returned" three of the items as not described or defective. Each time I am given a refund within a few minutes of requesting it. The refunds are for the full price, bot the "sale price." Look at the refund I got for the meter. I paid approximately $2.14 with "tax" and was refunded $3.86, more than I paid.