Rega RB-300 Counterweight

There seem to be several choices when it comes to counterweights for the Rega arms. Are there any differences between them? Please post your comments.
There are many choices, but one fundamental dimension of difference is whetehr the weight is underslung, so that the center of gravity of the arm is below the plane of the arm, or "in-line". There are posts on the asylum and here as to why underslung is better, and as to why it is worse. I found the "worse" view more persuasive, as a theoretical matter. But that's not wrth much, when it's sound that counts!

For what it's worth, I got a brass modded "in-line" counterweight rb250, and it sounds great. Some have complained about an tiresome imbalance in favor of bass in the underslung weights.

Lots to read on this.
I bought the Expressimo Audio Heavy Counterweight for my Rega RB-900 about two years ago, and posted a "rave" review for it, saying that the improvement it made to my turntable/tonearm combo was NOT subtle, and was the most significant "tweak" to my analog system I'd ever experienced. Since that post, the Expressimo Counterweight has been updated. I do not have any experience with any other counterweights, but on the basis on my experience with the Expressimo unit, I enthusiastically endorse it!

If you want to read my full original post, here's the link:
Use the Michell Technoweight; works great on the rb300 with Audio Note silver wiring.
OK to totally endorse all of them I have heard(owned) the Heavyweight and the Kerry Audio F2 counterweight. I prefer the Kerry model, just my 2cents.
Second the J.A.Michell counterweight. Totally different design and all weight is placed below the center line of the tonearm center horizontal plane. I have it on my RB600 and what a difference it made in detail, base response and clearity
When re-reading al the past posts on this topic, there is a consistent mention of each member's favorite.
My favorite is the Kerry Audio F-2 Titanium Heavyweight Counterweight. If you go back to my many posts about this tweak, it upgrades the analog vinyl listening experience so much that the praise seems impossible to believe. But, the praise is pretty much repeated by all owners, and by reviewers who get a number of companies to lend product for comparative testing.