Thanks, MX! I do note that the second item is described as "660 watts," which kind of limits its' use as a fuse holder.
I am quite sure that a given item, when presented to UL, will be tested to different standards, depending on whether it is described as a "luminaire" or a "fuseholder."
I will also concede that there are robust lampholders, and rather (shockingly) flimsy fuseholders.
I am not as enthusiastic in my condemnation of this practice (using a lamp holder as a fuse holder) as some are- but there are limits to the "field endineering" that is appropriate.
Just because the fuse fits doesn't make it right. One would hope to find branch circuit fuses in the fuse box, not tacked on to a remote disconnect. (BTW, the fuse holder was in no way associated with what the disconnect served). The holder, and fuse, are exposed to the weather. With the fuse removed, you had a live point directly exposed to passersby.
I suppose that, were one to mount such a fuse in a panel, controlling a circuit associated with the panel, I wouldn't think twice about it.
To borrow a phrase from TV: "Don't try this at home!" :-)