Bear,
USB scopes are usually advertised at total magnification. As a rule of thumb optical is 50% of that. But it's anyone's guess what an individual scope is.
I suggest you check out Amazon where some reviews might give you a hint of actual performance. You might need one said to be 400X, to have true 100X optical. You have to make sure the software is compatible with your operating system.
If you get a higher powered scope, I'd guess around 300X optical, I can tell you how to modify it to check for stylus wear. I used to use an AT scope for that. Top mag was 500X. Some of the microridge tips are so small you can hardly see them at 100X. Those old Shure scopes were mostly used for spherical or elliptical.
If you get one of those, it would be nice if the lamps can be switched off and the scope still operate. You need high intensity side lamps to check for wear.
neo