I highly recommend these, having bought a load for my Victorian-era GASLIGHT games. 2 Caveats though.
1) Buying from the likes of Amazon or eBay you can get these very cheap, however it's a bit of a crapshoot as to what exact sets you get. There are two different sets - tank engine & carriage is one, locomotive & tender is the other. And there are three colour options - red, blue and green. If buying from vendors who don't let you pick your colour, you might have to buy quite a few sets to get the right mixture of loco, tender + a couple of carriages in matching livery, if you're not planning a total repaint. Also be advised the engines are also sold on their own, without the tender or carriage, so make sure you know exactly what you're ordering.
2) Railway purists will grimace at the locomotive. It has a generally European appearance, but with an American-style cow-catcher on the front. I'm no rail expert, but that just looks plumb wrong to me, and if you want something that looks more at home on British railways, some remodelling work will be required.
But that said, I love these little trains. I think the carriage sizes are much more wargames friendly than those in the Poundland trainset.
Dr V