Mercian's Demonstrator Pens

This (bad) photo shows my current 'fleet' of 'demonstrator' pens.

L→R they are:

• Lamy Vista (my first Lamy pen, and one that I have had for long enough that I have almost entirely worn-off the sticker on the end of its barrel that said 'LAMY');
• Pilot Prera Iro-Ai green, with 'EF' nib;
• Pilot Prera Iro-Ai black, with 'F' nib;
• Pilot Prera Iro-Ai red, with 'M' nib;
• an un-branded Chinese-made pen.

That last pen has a folded steel nib with no indicated nib grade.
I bought it a few years ago - with two included cartridges - for 'fully' £0.59 in a bricks-&-mortar shop here called 'Home Bargains'.
You can see that its clip is broken (its only utility is as a roll-stop. Cf the clip on my Pelikan P480 Pelikano).

It wrote perfectly acceptably with the first of its included cartridges. At this price, I was frankly surprised that it even wrote at all.
It is rather small for my paw, so I have not yet used its second cartridge of (unbranded) black ink.