First new "thingy"
Metal-bender dies useable in a vice or with a fly-press. The magnets are to assist setting-up and help prevent them falling to the floor, which won't do their edges any good.
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Second –
Yes, it is a Keats Angle-block.
Although its primary purpose is for holding work on a face-plate or Te-slotted saddle / cross-slide, it is quite a versatile "thingy" that can also hold for example, a work-piece vertically on a mill or drill table.
A book on turning would be a better bet for information than the vagaries of You-tube. The "it seems" may just boil down to whatever single-project videos you saw, and their makers' available equipment – and opinions. I do have one, and bought it new only a few years ago. I don't use it very often but that's not the same as no-one using them "these days".
It use is fairly intuitive. The slots are for the bolts clamping it to the machine, the U-bolted Vee-block clamps the work between itself and the fixed block.
For some purposes on the lathe it is better to wangle the U-bolt off its block and use instead two flat bars with bolts and nuts; or bolts tapped into one of the bars rather as on a tool-maker's clamp. This will reduce the amount of projections twirling round. (Mine takes a bit of wangling as the loosened U-bolt legs splay slightly!)
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Noel – Shouldn't that be "Next slide please" ?