I would not worry to much about the aluminum material used even cast alloy that is CNC'd will hold up. When you torque the entire assembly down to spec its going to be real solid, if anything the first thing that would crack would be the bell housing of the transmission.
But as i have learned everyone on this forum drools over the minute detail of things..
Based on the images, price point, and location of PMC (Poland) if i were to guess they are using Dura Aluminum 2017 grade. Which is very inexpensive aluminum material but strong enough to make alot of nifty alloy bits.
Here is some info of 2017 vs the US industry standard 6061.. you guys can decide if it's worthy...
http://www.makeitfrom.com/compare/2017-T4-Aluminum/6061-T6-Aluminum/
For me the alloy used is good enough for an adapter flange application but not ideal of it's being subjected to rotational forces like a wheel spacer or flywheel. If PMC only supplied the supporting parts then they would actually sell some of these...
Supporting parts:
1. Flywheel ( you will either need a button style flywheel or a new flywheel made from scratch)
2. Clutch (which one, what stack height)
3. Throw out bearing style? mechanical or should a hydraulic version be used?
4. Trans Mounts to make sure it all lines up
5. Drive shaft adapter flange
With out those parts you can't do much with the plate... they should offer a working kit vs just a plate.
BTW they keep costs down because when they CNC a part it's not finished so basically it's a quick rough cut not a slow detailed cut you can tell by the pictures.