Calibration Slides

[Keiland]

Can anyone offer some insights on which model of calibration slide they use, I've heard of some differences between them, and that the link on the miniscope page links to a large selection from Thor.
I was thinking about the High-Frequency NBS 1963A Resolution Test Targets, 2" x 2" ; here: https://www.thorlabs.us/thorproduct.cfm?partnumber=R2L2S1P1

Any cheaper alternatives?
Thanks