Sigma Metalytics Precious Metal Verifier Bullion Set

They are two different things... the Fisch type ones are portable, the Sigma is not. Unless you are buying high premium numi stuff that you really don't want to take out of capsules, you can get peace of mind for a lot less...

$35 for a portable plastic tester of 1oz gold coin diameter/thickness/weight:
https://goldcoinbalance.com/

No fake coin of the same metal content can pass weight, diametter + thickness, and ring tests. That is a matter of fact. Nearly all fake coins will fail on weight, so that's the most critical (and why you want digi scale over just plastic balance). All fake coins also fail on ring test, but that is the hardest for some people to do. If there is ever any doubt, just don't buy it.

Only a very good tungsten fake could pass both weight and diameter + thickness (but it would fail ring test miserably on gold or silver, and fail magnet for silver also). At any rate, I see no need to spend $1000 or anywhere near that on anti-fake equipment unless you run a numi coin shop (in which case, you still need the weight/thick/diam tests anyways). The only advantage of Sigma is that it can test through capsules, but that also makes you lose the ring test, which is the best cheap test of all. You would also need loupe mag and the ability to use it... since there are plenty of fake 999 silver or 22kt or 24kt gold coins that are copies of rare numi dates.

...When it comes down to it, all you need to test basic coins for metal content is 2-3 basic things:
-pocket digital scale (to test weight)
-a real coin of the same type (to do comparison of look, diameter, and thickness, and to test ringing)
...The plastic balance tester is just an added bonus, yet is nice to have. The Fisch or similar devices make testing thickness and diameter faster and easier (in case your eyes are having a rough day), and it can do a basic test of weight (but not as well as the digital scale).

For silver, the magnet slide test is also good and dirt cheap. It probably costs you only a couple bucks and works well.

I do have an antique brass sovereign balance also, but that is more for décor (although it actually works impressively well... clearly the prototype from which Fisch and others were later designed to emulate)...