I almost went down the path of buying a Chinese detector off Aliexpress probably around 3-4 years ago, mostly because I had not researched what I really was after and also because buying a Pulse Induction or even a good VLF machine was out of reach for me (I briefly had a GPX 4500, but it was pinched 8.( ) I figured I might be able to get away with buying something sub $1000 and have a chance at getting a good machine, even though the Xterra 705 was staring me in the face the whole time. Mike you say "it's not scientific, there are no case studies" but that is incorrect, there are plenty of reviews on Youtube for most of these cheap clones, and none of them perform well. There are also countless stories on other forums of punters being duped by junkers, stories of people paying for "Genuine Minelab" to find they have no better circuitry inside than a Casio 100D calculator. Looks at how many have come up on Gumtree the last few years.
The Minelab and Garrett knock offs are one thing but there are plenty of generic ones available as well, many around 7KHz. They label them as all rounders too good to be true (GOLD NUGGETS, TREASURE, COINS!!) claiming absurd depths of up to 3.5 metres. Most of the time their tests are an iron plate (30cmx30cm) buried 30cm underground in dry soil or air testing a US quarter. Sure you might find a few spendables with one but other than an obvious sunbaker you are not going to find gold, you probably have the same chance detecting gold with a tinfoil hat.
Don't waste your money on one of these junkers, something you have no comeback on when it, A wont work and B falls apart. It's like you asked the forum for guidance then was not happy when you were told these things are nothing but junk or childrens toys. You have to respect some of these guys on the forum who have responded to your enquiry, they either do this for a living or have spent $1000's on this hobby and know the ins and out of every decent detector on the market. Some of these blokes have multiple detectors from Minelab, Garrett, Whites, XP, Makro, Fisher, Teknetics, Tesoro and they surely know what they are talking about.
Even a Minelab GO-FIND 60 will outperform I'm guessing 95% of these machines. I would only allow that 5% out of hope that one or 2 of the ones on the market might actually work.
Buy a Xterra 705, you can even pay them off with Afterpay or Zippay in some stores.