I have used them for times when I don't want to worry about damaging a good halter. They're OK for turnout. If you oiled it nicely, might do in a pinch--we're all on some sort of budget in this day and age. Not sure what you mean by showing--for in hand classes, or just to have something fancier than rope or nylon webbing on the show grounds? They're not very durable. The leather is more like cardboard.
Have been a Gatsby halter owner since the early 1980's, & still have some of those old halters. LOVE Gatsby as an inexpensive everyday halter. The leather is nice & supple, strong - but not so strong that I don't doubt it would give way in a true hysterical emergency. But I don't turn out in halters anyway.
I also like the fact that they come in a full array of sizes - 2 foal sizes, yearling, Arab, Cob, Regular, and two "oversize" sizes. The foal halters are particularly nice because they're not only classy looking, but the leather is soft enough so that rubs on tender skin are never an issue.
Also in their favor for me is that many local tack & feed stores carry them, so I don't have to mail-order, although I don't mind doing so if I need a particular size that isn't carried locally.
(Oh, & I also have two Gatsby bridles that I've also owned since the 1980's. Both are still in lovely condition.)
I like them for turnout halters when I can get them cheap (like under$20), I don't think they're really nice enough to bother putting a nameplate on for show. For a nicer show halter, I spend about $50 at Fennell's for a very nice halter suitable for a nameplate. I've had Fennell's cheaper turnout halters where the brass ring wore out before the leather- years and years of use!