I love most Castle Forbes stuff but I feel their Pre Shave is just ok and therefore not worth the high cost. It's an unusual scent too, has a slight almond scent. It does soften stubble but wouldn't say it adds any extra slickness.
The Fitjar stubble softener soap bar is really good at doing exactly that, softening stubble. Just get it wet and rub over the stubble. Then use your hands to rub it in and it creates a surprising amount of lather from such little soap (Which makes you understand why the bar is smaller than you expect when you first open it). Leave it on while you lather up your shaving soap/cream. It's quite clay like in its scent.
Again I don't feel it particularly adds any under layer of slickness.
It actually makes a great face cleaning soap too so it's kind of a two in one product.