I use these, the one on the left is nice and is very strong and simple, will never break.It has a double beam, I got this one from Wizards Racing.
Then the air one was built by Mike Troxel, Melanie Troxel/Johnson Dad. It's also bullet pruff but big bucks. Then one is for on the motor, then a homemade one and a spring tester is what the other ones are.

I also use one like this for on the motor, doesn't fit all heads, but is nice for changing springs on the motor in the car.