The half converted rifles suck. You also need a handguard retainer for the standard handguard. It is a pain to put a milspec one on but you can bolt one on. Not all saigas are threaded so you nary have to thread the barrel for a break (sic). What you might want to do is spend a little more for a rifle that comes with the front end converted.
I assume by half converted you mean a gun with the factory saiga hand guard? How exactly do they suck?
Give the small difference for the gun's you linked to it is likely worth it just for the threaded barrel. The tools to thread it cost about $50, although they could be resold or reused to off set some of that price.
The factory AK front end gives you more options for aftermarket handguards. There are longer ones available that extend up to the gas block if you are so inclined, and they are not made of flimsy plastic and don't have the goofy bottom sling swivel attached to the barrel like a factory Saiga one does. With the original Saiga style handguard, you are basically limited either to it or the Tapco replacement one.
You are not real familar with AK handguards are you? Any of the extended handguards I'm familar with do not mount with the handguard retainer, some even require removing it and thus they can all be put on a saiga just as, or even more easily than any other AK variant.
You think the only option for the saiga is the Tapco? That is simply incorrect. Just off the top of my head there are handguards from SGM, TWS, Midwest industries (4 different ones from them actually), chaos, ultimak, etc. The best (IMHO) hand guard options are as easy to mount to a saiga as any other AK.
As to your other points I'm not sure I would call the saiga handguards flimsy. It is not. Cut into one and you'd it has metal reinforcements inside. I've never even heard of one breaking. As to the sling swivel, it is easily removed. If I had my choice between stock AK handguards and a stock saiga handguard I'd take the latter simply because it allows one to grip the rifle further out and thus have better control over it.
so you don't have to worry about milling a new pin notch, moving the front sight back, and threading the muzzle like you do on a regular Saiga if you want to have a threaded muzzle.
There are a few ways to go about threading a saiga, however, only the 308 requires moving the sight back. Most people tend to cut the shroud and if there are no factory threads underneath they then thread it. The gun linked to earlier does have a front sight block that allows for a cleaning rod too though.
Some folks are moving the sight block back against the gas block in an effort to shift weight to the rear so the gun balances better and there is less mass on the end of the muzzle adding in transitions from one target to another. Some people prefer this to going with something like a bolton gas block. Some are moving the sight block back in conjunction with shortening the barrel and pinning a brake or flash hider like on the gun below.
BTW that handguard is on a saiga.
