Which Digital Level Gauge to buy?

Dougdeacon.
I agree with your comments.
Certainly about the phone apps.
That's why I would love to find a level table to see how accurate this app/phone is.
And yes, you really can get a good result from a bubble level but I would suggest not nearly close to a good electronic devise.
Since purchasing my SME 20/12A and Soundsmith Strain Gauge cartridge I have become acutely aware of how the slightest changes in geometry and level radically affect the sound.
With this kind of money invested I feel that a couple of hundred bucks more to ensure a precise level is money well spent.
Technique is king...but a great tool used correctly is the ultimate solution in the end. And which of us doesn't love a great tool :-)

We're all great tools on this forum!

the way I see it is if the turntable and platter are not perfectly level, all of the other settings are compromised in one way or another, especially on a unipivot arm. I questioned the expense when ordering the cartridge man, bit after receiving it and using it, is now indispensable. I also use it to set up my record cleaning machine, a Loricraft.

"I also use it to set up my record cleaning machine, a Loricraft." .... good grief

Loricraft has a tonearm with counterweight and works better when the platter is level, and is more sensitive to out of level than a VPI type machine.