Neither of those product would be recommended. The one is non hardening so you'll have a problem getting a finish to adhere. The other is normal wood putty and will shrink back badly and will not fill the pores very well. If the person this project is for only has those available, I am guessing they are limited to hardware store materials. At that point, I would use clear epoxy as a grain filler, it is cheap, and fairly easy to use and is easy to find. But you can not stain on top of epoxy. You would have to stain first, but you may have problems with the stain bleeding into the epoxy. Try a scrap piece first. With epoxy you may want to use a tinted clear coat to get the black transparent, but that will be hard to find at a hardware store, more than likely you'll have to mix it yourself. But you can spray that over the epoxy.