I have a hs2000. Bought it for the same reason as you, wanted a cheap 9mm plinker. Have put 150 rnds of Greek 124gr through it so far without any problems. Shoots good and seems well made. The trigger for a DAO was pretty good too. The hs2000 seems to have been accepted well so far so finding parts down the road for it probably won't be a big deal. I haven't had any problems with rust. Don't think it is a problem as long as basic care is applied to the pistol. I also like the grip, it is quite good.
The only thing that is weird about the pistol is that the extractor is sort of like that on a 1911. Its not spring actuated, but works based on the elasticity of the steel. Don't know if this would ever be a problem down the road. After 150 rnds, I have also noticed some odd sort of wear on the outside of the barrel where it locks up to the slide. There seems to be a lot more wear here than would be normal, at least more than I have seen on any of my other pistols. There is a groove where it locks up and there are dings in the barrel were the slide recoils backward. They are not large and I haven't heard of anyone having problems related to this phenomenon. Just seems like the barrel steel might be a little soft. Don't think it is a big enough deal to affect reliability or accuracy.
As far as high caps go, I found the s&w 59 series mags to fit the best in the gun. You will have to modify the mags though, a hole needs to be drilled in the front and filed to fit the mag catch. The follower step that engages the slide stop will also have to be cut down some so that the slide won't lock back on the second to last round. Beretta mags will also need to have the mag catch drilled into the front. This can be a pain, but isn't very hard to do, just buy some promag mags for $15 and go at it. As far as the TZ99 goes, you can buy factory high caps for them for about $30. This would be much easier but will cost more.
The TZ has a aluminum frame and doesn't have a accesory rail. The HS is rated for +P+ ammo, not sure about the TZ. Both would be fine buys, just a matter of tastes I suppose.