Does antiskating matter with spring disabled?

Yes. AS is different from VTF. You still need to counteract the tendancy of the arm to twist toward the center of the record.

I tried one of these counterweights on an RB-300 and went back to the original -- liked the sound better. YMMV.

I am using the Expressimo heavy counterweight on my Rega RB-900, and have the VTF disabled (by turning the VTF gauge all the way up). And unlike Dopogue, I was really quite amazed at the improvement wrought by the Expressimo counterweight.

Fact - When you install the new c/w and disable the VTF spring you will have to adjust VTF by measuring it with a scale. (This is good.)

Fact - For the scale to work accurately you must zero out AS.

Conclusion - You will have to reset AS afterwards.

Recommendation - The AS device on Rega arms is notoriously inaccurate. Most people find the optimum value to be lower than the scale indicates. Nsgarch's world-famous visual AS-setting method is easy, effective and free. (I'll let him type it - again!)