Rega P 25 and Express Machining Counterweight

Theo - I just added this tweak a few weeks ago to my P25/RB600 and am amazed, particularly with depth of field improvement. I am using a Benz LO4 with a Pass Aleph Ono. I also placed 2 old cd's under the glass platter to get the negative VTA required. Make sure you lock out the spring in the tonearm and set your tracking force with a scale.

Ditto to all the above. I am using one on my P25/RB600 combo, as well as my OL/P3 combo. Have not changed the one on my P9/RB900, yet, because I want to upgrade to an RB1000, when I can.
I would not have believed that eliminating the stock weight could actually make that much difference.
It is a relatively inexpensive upgrade, and well worth the money. Go for it!

I had excellent results on my OL arm with the Heavyweight.

I used to have a p25 with rb 600. It's a big upgrade. No downside. Plus it's easy. Let me know if you have any more specific questions....

I added the Express Machining "Heavyweight" counterweight to my Rega RB900 about 2 years ago (I have since sold the RB900 and replaced it with a Rega RB1000), and I was VERY pleased with the improvement it made. Infact, I wrote a review about the counterweight here on Audiogon, which you should be able to find in the archives.

In short, I strongly urged owners of the Rega tonearms to buy this replacement counterweight, as the improvements it provided were significant.