Both the Saiga you linked to and the Arsenal are both "basically" the same rifle, built in the same plant, to the same standards.
The Arsenal is specially built for Arsenal to make it easier for Arsenal to do a conversion to full military AK configuration. It comes in as a barreled receiver made to be easier to convert.
The Saiga you linked to was imported as a complete full commercial type rifle and partially converted to a semi-AK configuration.
The linked rifle was basically converted from the trigger group on back, with the entire front of the rifle left in original commercial sporting configuration.
Both will shoot the same.
I'd ask the company if the rifle will accept standard AK magazines or if it needs the special Saiga commercial magazines. If it needs the special mags, you can't use military mags unless you do further conversion work.
Bottom line, if you just want a shooter and don't really care that it's not in full military configuration with the hand guards and muzzle brake, longer range rear sight, and the plugged holes in the rear of the receiver, the semi-converted Saiga is a good rifle at a good price.
If you want the closest thing you can get in appearance and function to a Russian full-auto AK, the Arsenal is the best.