This is a fine place for that question. To tie it in to the Flexner discussion, one thing to wonder is what exactly is in it. Flexner correctly points out that labeling is often either misleading or at least uninformative.

If I'm looking at the right product online, I suspect it is a polyurethane based product, which is likely why it hardens. You could check the sds.

The bottom line, in my opinion, is that if it gives you the look and feel you want, then go for it. It will undoubtedly be simpler than a true slakum oil finish.

On the other hand, as Damascus and Salopian pointed out, there is a reason the "best gun" makers continue to use oil finishes. The look and feel is very difficult to replicate in any other way.

If I were refinishing a vintage gun with hand checkering, hand engraving, a hand shaped stock, etc, I would do the extra work of putting a hand-rubbed oil finish on it. In fact, on a vintage best gun, I would be reluctant to put anything but traditional ingredients in the mix, even if the addition of poly to the mix would increase durability and hardness.

And to the point of the original post, if you decide to use a boiled linseed oil slakum, there is nothing in Flexner's book to say you'd be wrong, as far as I can tell.

Jim