I use RCR Box springs. Works great:
- You do not have to lock/unlock (walk mode) springs.
- RCR Box contains 3 springs of different stiffness, so you can adjust stiffness without limiting max travel.
- Max travel a bit bigger.
Spring vs Tongue. Tongue has more of static stiffness, Spring is progressive.
When I use orange spring with dark grey tongues, it is quite hard on shin of the back leg, but makes toe side turns more powerful. Black spring relives quite a bit of pressure off shin (even with dark grey tongue), but you loose a little bit in control.