There was a small entry on the reptile house blog about the similarities of the mdd and the rwa hop up units.

Which one is the best. I want to buy once.

The MDD had some problems when I got it. It still has problems, but I think removing the upper pin entirely or cutting it down and gluing it in place so it does not contact the adjuster at all is the solution. I see no reason why it should be there, but all the designs of this type do it. You only need contact at the bottom of the cage. Having contact up top restricts movement of the cage, limits adjuster size and durability and reduces consistancy.

With this in mind, none is better than the other. Do they perform better than a standard chamber? No, absolutely not, and a case can easily be made that they have a large weakness by using the upper adjuster pin. But they do give you adjustability without dropping the mag and without a 1.5mm hex key.

The charging handle needed to be filed down to accomodate the wheel, but this was with a real Daniel Defense charging handle in a real Aero Precision upper. A DYTAC charging handle suffered the same fate.

I have some STTS chambers enroute to me now. I will try one of them and see how the wheel fits in the upper.

I am still running the stock hop up on both PTW but would like a better one if it does exist.

Does the upper and lower pin not float and move the nub up and down equally and hold it firmly?

I guess, the better question, what would make the best design for a PTW hop up unit?

Stock chamber with modified adjuster is still the best. Works well and is time-tested.

The pin does float but with the increased dimesnsion of a modified adjuster, it provides counter-pressure to the top of the adjuster. There is no need for that, and is undesirable behaviour.

I just increase the tension on the cushions under the adjuster to get lots of pressure when the hop is set to it's optimal point.
The ideal hop up is a fixed hop set exactly where you need it to be.
Either way, nothing wrong with the stock chamber. The MDD style is just for better accessibility.

Wrong. The PTW hopup is designed to roll around the BB. If it is fixed, like with a poor-fitting cage, the only pressure is from the compression of the adjuster material. And that is short lived. The end result is a torn adjuster.

The cage needs to move, even if only slightly. Then, as the adjuster becomes permanently compressed in the middle, it becomes very consistant and longevity is very good (think years and hundreds of thousands of rounds). Fixed adjusters fail very quickly.

I have seen it too many times to count.

I have seen ball bearing on the roller pins. Is that functional or hokey pokey?

I have never seen that.

Too much vertical movement will give you inconsistent hopup. And using flat hops, the adjuster has no need to move up and down.
The most accurate systems are those with the least amount of moving parts

Too much is bad. Carefully executed and minimal is fine. In a PTW with a properly fitted adjuster which must be done each time with each cage and barrel is best.

Perhaps, but that is not how a PTW is designed to operate. And when done well, range and accuracy are unparalelled.

Here it is. I forgot where I got the image from but it does show bearings unless I am seeing things.

I don't know why you'd ever want that, hopup is created from friction, if the roller rolls where the BB goes, no backspin will occur. That's why we glue the hop rollers in place.

Bingo!!!

So what is a "modified" hopup anyway?