I hear my theme music being played...
I have owned all the major brands of AK - RS, E&L, LCT and GHK. Real Sword externals are excellent but not a major step above LCT and E&L, I would say E&L externals are better than LCT but they do rust. They are just as good. Internally probably better. Real Sword AKs also seem to have a persistent issue with feeding of BBs, happened in mine and I have seen it in others. For the price difference stick to E&L or LCT. Also, bear in mind that the RS receiver is ever so slightly different length than an E&L or LCT so may prove an issue with aftermarket gearboxes etc if you are planning on switching out any internals.
Re the question about receivers. As Sniper said, that receiver type is common where you have a fixed stock a la AKM. Where there is a folding stock or underfolder it will be a different type of receiver and lack the stock tang. The exception to this is the Romanian AIMs style side folder which has the same type of receiver tang as the one you showed. I have, for instance, replaced my GHK AKM wood stock with a GHK AIMs stock and it slots straight in.
Any other q's?