Depends on your use case. I wouldn't use it over a Macbook or Microsoft Surface because I need to use x86 compatible programs, but if you can get by with iPadOS, and you can stomach the high cost, go for it. If you want something cheaper but almost as good, a used 2018 iPad Pro should suffice for most people.
Personally I like apple products, at least better than google. But Iike the previous Ipad pro a12x and the now a12z have no real difference. So if you are using it only for benchmarks, I think better not. Personally I think it's a cool chips. Huawei kirin 980 and 990 can only run geekbench to 3000, and have little room to overclock over 3200. While A12z can get near 4600, 4700, maybe a bit more if you manage to overclock it.
Some Android phones will allow you to choose a power profile, which can affect the speed of the processor. If an Android phone doesn't have power profiles, you can root it to overclock it. Apple products are more difficult to jailbreak. If you're able to jailbreak an Apple phone, it's doable on Apple products, too.
I'm sure it'll make for a wonderful paper weight. Yes, not only can you overclock, you can even undervolt. Been a thing for over a decade.
Considering the new magic keyboard case that's gonna be available for it, I believe it's quite worth it. And you can even use the cursor for it, so why not?