I guess its worth it if you want an HK and have the money. Without a selector and being able to stock it, I really dont see the point.
Now, if you've got the bucks, and a trigger pack, its probably going to still be a lot cheaper than buying a transferable MP5.
My buddy picked up a couple of the Zenith copies used for about $1500. They seem well made and pretty close. They seem to shoot without issue. Cool guns, but like the official HK, still kind of pointless without the selector and stock.
I think what has made guns like these from HK worth what they get now are the bans of the past, HKs attitude towards us lowly civilians there for a while, which with the bans, severely limited the number of guns available, and now, they arent the hot number they once were, and they just haven't flooded the market like they did early on, likely due to other things grabbing the market, and they are aiming them at a certain market. A lot of people who grew up with things like them back in the 80's and 90's and couldnt afford them then, are a bit older now and making good money or retiring and did well. That gun now, would have cost 10 times less back in the 80's.
The other thing I never understood with the HK's, as far as the ATF goes is, these guns are very easy to convert, and for a long while, the parts needed to do so were readily available, and the ATF never seemed to make any effort to stop them from being sold.
I bought an HK94 back in the mid 80's when they were selling for $450. Just before the machinegun ban, I sent it to Fleming and had it converted. That cost me $350. So for $800, I had a "sorta" MP5. What was different was, it didn't have the "third pin", and I couldn't drop a true MP5 lower or trigger pack in the gun, due to the differences in the recievers. But I could drop my trigger pack and bolt carrier into any HK94, and it was a full auto. My gun was a registered receiver machinegun, not a registered trigger pack. The registered trigger packs became the big thing, and that was something that got Fleming into the trouble he got into over them.