I can't confirm for 100% as I have other purchases to make so I've not purchased one of these to check. From what I've found out and to expand on Dave's post:
Metal shock absorbers - might mean metal suspension, again i order my panzers from heng long with that as standard
I believe these have torsion bar suspension and a metal lower chassis. In all likely hood this also means metal suspension arms.
Recoil action when it fires a bb - does he mean whole tank recolis or just the barrel. the usual is the whole tank recoils
I am pretty sure, as Dave said this is the newer airsoft units Heng Long is putting out, as shown in a thread by Big Wheels they have a micro switch on them and are connected to the RX18 so that when it fires a BB the whole tank recoils. I may also make the firing sound but not 100% on that yet.
There is also a fairly large amount of mid/late production detail parts that are presumed to made from metal. The late production wheels could also be metal but without having one to check it is an unknown.
Looking at this way, an upgraded metal Tiger (pro version smoke and sound) retails at around £100-£120. For the extra money you are buying a lot of extra upgrades, plus Zimmerit that would cost you a great deal more in individual parts. Although quality wise nobody will know until they purchase one.
A lot of what people have said on the forums is pretty much conjecture about who Taigen are as the people I've asked don't know who they are. If they were associated with Heng Long, other than using their products, then the people who buy from Heng Long don't know about them.
They don't, as yet, have a web presence. The only thing I can think about is they brought their products to a toy fair.
I think due to the price of them no one is wanting to risk buying one!

When I get one I will put up the info, I'm sure you are all as interested in what makes these things tick as much as I am!