Pico is very friendly when it comes to using non-Pico branded accessories. Through the use of custom probes, you can create a scaling for any probe to read out on the screen in units of current, pressure, or whatever.
That being said, not all accessories are created equal. Take the basic 20/60 amp probe for example. Pico went to some effort in the design of this probe to make it more resistant to underhood EMI. This makes them better for automotive use. While these may look similar to other probes, the Pico branded probe is nickel shielded and has a longer shielded BNC cable.