Hi Elvin
Yeah I've been in contact with Powerflex a year or so ago. Main problem seems to be the omega has a 14mm bolt hole. Almost all of there ball joint type rearward bushes are for much more popular front wheel drive cars with a 12mm bolt hole.
With the size and weight of the omega I'm not sure I fancy fitting a smaller bolt, especially the way some members wang these cars about.
Meyle web site lists the p no. And dimensions of the oe rubber rearward bush
614 035 0010
Height 46
Inner diameter 14
Outer diameter 49
The only bush I can see that (Meyle) they make, while cross referencing sizes, that comes close is Corsa c that is also 46mm high, but the outer diameter is way too big at 60mm with a 12mm bolt hole.
Unfortunately the omega rearward bush does not cross reference with any other vehicle, the hope being that a more popular car might have a poly bush in production, like the BMW fronts.
Also, the amount of vertical travel on some of the more basic designs, like golf iirc, means there's also a chance of the ball popping out of the bush, so a metal case type is much preferred I guess. If only a suitable size could be found.

I haven't checked their web site for a few months now, so they may have released some new products recently that might work.