I can get my LT-40 to snap and spin with elevator and rudder input only. No aileron required, which is a sign that it is a true snap IMO. The CG must be back near the limits suggested by Sig, and the throws must be high. To get my LT-40 to spin I have to enter a snap at about 1/4 throttle and hold in the elevator & rudder. The plane snaps, then falls over into a spin. After a couple of rotations it I can idle the engine and it will stay in the spin.

I imagine that an Arrow would be even easier to snap/spin than an LT-40, but the CG must be back, etc.

They are not the crisp snaps one gets from a aerobatic ship, however.

I had a UCD, but found that it really didn't do great snaps. It has a very thick constant chord wing, unlike a pattern plane that typically has a thinner airfoil and a tapered wing - more suitable to performing a clean snap.

The Great Planes's Venus is one to consider if you are looking for an ARF.