I want to build an oscilloscope octopus tester. What's the best design out there? Would like a clean looking unit with the features that make it more useful.

A FET blower.

There are any number of parts that can be damaged or destroyed using 'in circuit' testing.

A simple FET is one of them that is commonly blown.

So got a favorite design to share of FET blower?

There are thousands of curve tracer designs of various types out there.

In circuit testing of active devices is just about always a bad idea,.

It is all to easy to damage active parts ALREADY installed in a circuit this way.

Take the part out of the circuit and test it.

Or analyze the circuit and figure out HOW it should work and using an oscilloscope and mutimeter verify it is working correctly.

It is referred to as 'debug and test.'