FWIW I have been an Asia Miles member for a long time. I've fairly regularly been able to utilize their miles to book award travel on Cathay. I have never tried using a partner. The types of awards I have booked include:

1) Upgrade from coach to business on Cathay (fairly convoluted system to do that where you buy a coach ticket and then have to "convert" the record with the Asiamiles desk, but it worked)

2) Free business class on Cathay (worked quite smoothly)

For Cathay flights, their website has been fairly good about showing when things are available, and if not available searching for alternate dates that show availability.

As an aside, they have a nice "hidden" route between YVR and JFK, which I use fairly regularly.

Some random notes to be aware of:

1) They have upgrade awards for Cathay, Dragon, AA and BA - but not for the other airlines. But the upgrade rewards require a higher fare class than the most heavily discounted.

2) Awards are mileage based, so you certain "odd" routings would take more mileage if they go over a threshold.

3) Elite levels work differently. It isn't automatic. You need to be a separate member of the Marco Polo Club for oneworld elite benefits.

Generally I've been fairly happy with Asia Miles as a program and have certainly enjoyed the Cathay flights that I regularly take.